Illegal immigration has become a major issue in the United States in the 1980s, and continues to be a highly visible issue.
Illegal immigrants pay sales taxes and gasoline taxes; most are too poor to pay income taxes. Many use fake Social Security numbers and pay Social Security taxes but are not eligible for any benefits. Many use tax-payer funded services such as health care and schools.
Numbers of people
Pew estimates about 12 million illegal immigrants lived in the U.S. in 2004. However, many are afraid to use available services, such as domestic violence shelters, out of fear of deportation. Many illegals cannot speak English.
Arguments favoring it
No one else wants those jobs anyway
Illegal immigration is defended, saying that immigrants are simply coming to take unskilled jobs that better educated Americans avoid, such as picking fruit and lettuce, making hotel beds and working in slaughterhouses. One could just as easily argue, however, that these jobs in part only seem unappealing to many Americans because of their association with illegal immigrants. Furthermore, not all illegal immigrants pursue undesirable jobs. In a recent case in California, a Hispanic man who came to the country illegally sought the right to take California's Bar Exam in order to practice law.
They need political asylum
A small percentage come illegally to escape political oppression, as legal channels are not open to them. Marriage to a U.S. citizen does not automatically gain one citizenship. When Army Spc. Alex Jimenez was captured by terrorists in Iraq, his wife was almost deported by the government. Strong public opinion allowed her to stay.
Where they come from
Mexico is the source of the about half of the recent illegal immigrants to the United States. Most arrive legally and over-stay their visas. Others cross the border mostly through the desert southwest or less often by swimming across the Rio Grande. Canada is another large source. Currently estimates show around 70,000 undocumented Canadian workers work in the U.S. They come over from the border with Canada along the northern part of the United States which is not nearly as secure as the southern border with Mexico.
Dispute with Mexico
The United States receives constant criticism from the Mexican government for its efforts to curb illegal immigration. And United States officials criticize Mexican officials for passing out handbooks on how to cross the border, saying Mexico is trying to avoid political and governmental reforms at home by encouraging its citizens to leave.
Under Title 8 Section 1325 of the U.S. Code, "Improper Entry by Alien," any citizen of any country other than the United States who: -Enters or attempts to enter the United States at any time or place other than as designated by immigration officers; or -Eludes examination or inspection by immigration officers; or -Attempts to enter or obtains entry to the United States by a willfully false or misleading representation or the willful concealment of a material fact; has committed a federal crime. Violations are punishable by criminal fines and imprisonment for up to six months. Repeat offenses can bring up to two years in prison. Additional civil fines may be imposed at the discretion of immigration judges, but civil fines do not negate the criminal sanctions or nature of the offense.
Illegal entry is not a misdemeanor in U.S. law, at the level of speeding. Those who are caught are usually promptly expelled from the country without penalty. However, multiple illegal entries can lead to felony convictions.
Legislative leaders in at least half a dozen American states say they will propose bills similar to a controversial law to fight illegal immigration that was adopted by Arizona last spring, even though a liberal federal court has suspended central provisions of that statute. 
Mexico and Mexicans - Escaping Socialism
Ironically, one of Mexico's harshest criticisms was a plan by the United States to make illegal immigration a felony offense, which would impose harsher penalties on illegal Mexican immigrants. Mexico's own laws make illegal immigration a felony offense in that country.
Many Mexicans have to come to the United States to work because for many years the Mexican government was socialist, being under the control of the Institutional Revolutionary Party, which limited economic opportunity and growth. Before 2001 there was frequent movement across the border. It was common to work in summer jobs in the U.S. and spend the winter in Mexico. Border security since then has become much stricter, and it is far more difficult to cross repeatedly. Therefore the tendency was to remain in the U.S.
An unintended consequence of the tighter border security is that millions stayed in the U.S. and did not return.
Like other immigrant groups, many illegals send money to their families remaining in the old country. In Mexico this funding is the second largest source of foreign income, after crude oil sales. It represents as much as 2.5 percent of the nation's Gross Domestic Product 
Canada and Canadians
Currently estimates show around 600,000 undocumented Canadian workers work in the U.S. They do not contribute to the U.S. economy in any way shape or form. Canadian citizens are not required to obtain Visas Unlike Mexican citizens, instead they have Visa waivers which last for six months. They take jobs from U.S. citizens primarily because they would be paid significantly less for the same jobs in Canada. (mainly in the construction industry.) The border with Canada is significantly easier to cross, due to several factors such as less Border Patrol personnel and a significantly greater border a 5,525 mile border with Canada compared (with 1,538 miles being added from Alaska 's border) to the 1,951 mile long border with Mexico. Along the border with Canada we have around 1,000 Border Patrol agents to cover the entire border, whilst on our border in Mexico we have around 11,000 agents.
The Reagan Administration gave amnesty to all the illegals present in the country in 1986. The "Immigration Control and Reform Act" of 1986 legalized the status of about 3 million immigrants which created a lot of Democrat voters. Other laws legalized the status of immigrants from Cuba and Haiti. In 2006 President George W. Bush and Senator John McCain proposed legislation to legalize the status of most of the illegals. The business and religious communities supported the idea, but grass roots opposition blocked passage in Congress and denounced the notion of "amnesty."
As the Bible exhorts people to be compassionate towards illegal immigrants (Exodus 23:9 and Leviticus 19:34), and as more Americans are Christian than any other religion, many Americans feel compelled by their religion to show compassion and caring for illegal immigrants, many of whom are trying to escape tyranny or poverty in their homelands.
Some conservatives oppose illegal immigration because it allows for immigrants to fall between the cracks of society thus making them more likely to commit crime or experience poverty. Other conservatives view illegal immigration as an exercise in a basic individual human right to pursue happiness. Illegal immigration is also economically damaging to countries because illegal immigrants will often work illegally for below minimum wage, resulting in job loss for legal citizens.
Advocates have long put a priority on gaining legal status for the children of illegal immigrants under the reasoning that most did not make the choice to enter the country illegally and have spent most of their lives here... [but] "we will not allow lawmakers to condemn our parents to second-class status,” Cristina Jimenez, managing director of United We Dream, said . “Our parents’ dreams enabled our dreams, and we owe our success to them and the sacrifices they made.” 
Crimes Committed by Illegal Immigrants in the U.S.
Among many others:
- 2002 - Ingmar Guandique, a Salvadoran in the United States, is currently serving a ten year prison term for assaulting two joggers in Washington D.C. is now suspected of killing Chandra Levy. The Levy case is famous because during the initial investigation her relationship with California congressman Gary Condit was revealed, ending his career. 
- 2005 - Raul Garcia-Gomez, shot two Denver police officers in the back, killing one. He fled to Mexico and was captured. However, the Mexican government sheltered Gomez until the American prosecutor agreed to not seek the death penalty against him. 
- 2008 - Diego Pillco, a 20-year-old from Ecuador, pleaded guilty to first-degree manslaughter of actress Adrienne Shelly. Pillco was sentenced to 25 years in prison. Pillco admitted strangling Shelly and then hanging her body to make it look like a suicide. The judge said Pillco would be subject to immediate deportation upon release from prison. 
- 2008 - Edwin Ramos, killed three people on their way home from a family picnic. Ramos had been arrested multiple times before the killings (once for mugging a pregnant woman), but the city of San Francisco shielded him from deportation. 
Where newcomers have settled
The amount of people immigrating to the United States illegally has declined since 2001. People who formerly moved back and forth across the border (working the agricultural fields in the US in the summer and wintering in a village in the winter) has declined, and instead they remain in the U.S. The estimated number of illegal immigrants in the United States in 2005 was about 12 million.  
$397 billion dollars have been paid to families containing illegal immigrants through social services since 1996. Most of the money goes to schooling for U.S. citizens and for children.
The number of illegal aliens who are in prison is over 300,000, about 3% of the total.
Sex offenders comprised 2% of illegals who have been arrested. Nearly one million sex crimes were committed by illegal immigrants in the United States, in the seven years 1999-2006. Each sex offender averaged 4 victims. 
Households headed by illegal aliens imposed more than $26.3 billion in costs on the federal government in 2002 and paid only $16 billion in taxes, creating a net fiscal deficit of almost $10.4 billion, or $2,700 per illegal household. Most of the costs were incurred by U.S. citizens, however, not by the illegals. On average, the costs that illegal households impose are less than half that of other households. In terms of welfare use, receipt of cash assistance programs by illegals tends to be very low, while Medicaid use, though significant, is still less than for other households. 
There are some 7 million illegal immigrants in this country who lack health insurance, according to the Pew Hispanic Center. 
- 83% of warrants for murder in Phoenix are for illegal aliens.
- 86% of warrants for murder in Albuquerque are for illegal aliens.
- 75% of those on the most wanted list in Los Angeles, Phoenix and Albuquerque are illegal aliens.
- 24.9% of all inmates in California detention centers are Mexican nationals
- 40.1% of all inmates in Arizona detention centers are Mexican nationals
- 48.2% of all inmates in New Mexico detention centers are Mexican nationals
- 29% (630,000) convicted illegal alien felons fill our state and Federal prisons at a cost of $1.6 billion annually
- 53% plus of all investigated burglaries reported in California, New Mexico, Nevada, Arizona and Texas are perpetrated by illegal aliens.
- 50% plus of all gang members in Los Angeles are illegal aliens
- 71% plus of all apprehended cars stolen in 2005 in Texas, New Mexico, Arizona, Nevada and California were stolen by Illegal aliens or "transport coyotes".
- 47% of cited/stopped drivers in California have no license, no insurance and no registration for the vehicle. Of that 47%, 92% are illegal aliens.
- 63% of cited/stopped drivers in Arizona have no license, no insurance and no registration for
the vehicle. Of that 63%, 97% are illegal aliens
- 66% of cited/stopped drivers in New Mexico have no license, no insurance and no registration for
the vehicle. Of that 66% 98% are illegal aliens.
- 380,000 plus "anchor babies" were born in the US to illegal alien parents in just one year, making 380,000 babies automatically US citizens.
- 97.2% of all costs incurred from those illegal births were paid by the American taxpayers.
- David W. Haines, Karen E. Rosenblum. Illegal Immigration in America: A Reference Handbook (Greenwood Press, 1999) online edition
- Pierre Hauser, Illegal Aliens (1990)
- Jeffrey S. Passel, "Unauthorized Migrants: Numbers and Characteristics," Pew Hispanic Center Reports and fact Sheets. (June 14, 2005), online
- Claudia Sadowski-Smith. "Unskilled Labor Migration and the Illegality Spiral: Chinese, European, and Mexican Indocumentados in the United States, 1882–2007," American Quarterly, Volume 60, Number 3, September 2008, pp. 779-804 in Project Muse
- Aristide R. Zolberg, A Nation by Design: Immigration Policy in the Fashioning of America (2006)
- TRAC REPORTS "Border Patrol Expands But Growth Rate After 9/11 Much Less Than Before Division Between North/South Border Little Changed" April 4, 2006 
- About Illegal Immigration, Right Wing News
- Congressman Introduces Bill to End ‘Birthright Citizenship’
- Higher estimates run to 20 million; see high estimate
- Illegal Immigrant Can't Be Lawyer
- http://www.immigration-usa.com/george_weissinger.html immigration Usa
- www.uscis.gov Immigration and Naturalization Services
- www.dhs.gov Department of Homeland Security
- Missing Soldier's Wife Faces Deportation
-  World Bank Report on Migration and Welfare
- Pew Hispanic Center report
- Illegal Immigrant Worker Sentenced in Slaying of Actress Adrienne Shelly, Associated Press, March 13, 2008
- Illegal Immigrant Worker Sentenced in Slaying of Actress Adrienne Shelly, Associated Press, March 13, 2008
- A Line In The Sand House Committee on Homeland Security
- The number of convicted criminal aliens in federal prison at the end of 2003 was 46,063; in state prisons and local jails here were 262,105.online
- The Dark Side of Illegal Immigration Violent Crimes Institute, 2006
- The High Cost of Cheap Labor Center For Immigration Studies