A little bit more on jobs....
"the defenders of illegal aliens — ethnic advocacy groups, employer groups, and church-based groups — often assert that illegal aliens only take jobs unwanted by U.S. workers. This is patently false because they are working in jobs in which U.S. workers are also employed — whether in construction, agricultural harvesting or service professions.
If the hiring of illegal alien workers is prevalent in a sector of the economy, as it has become the case in seasonal crop agriculture, the willingness of foreign workers to accept lower wages because of their illegal status acts to depress wages and working conditions for all workers in that occupation. This in turn makes employment in that sector less attractive to U.S. workers who have other options. The result is a form of circular logic, i.e., the more that illegal aliens are able to take jobs in a sector of the economy, the less attractive the sector becomes to U.S. workers, and the greater appearance of validity to the lie that only illegal aliens are willing to take jobs in the sector. Only by enforcing the immigration law against employment of illegal alien workers can this spiral to the bottom be broken and employers forced to restore wages and working conditions to levels that will attract U.S. workers and legal foreign workers."
Illegal Aliens Taking U.S. Jobs (2013)
This are is the most closely debated. The other factors brought up by RUBICON are right on target.