Fact: Illegals do take jobs away from legal folks. By deporting illegals it would free up jobs so that those that are here legally could get a job and have more money to spend. It also lowers the umemployment rate since illegals are not counted when officials figure out the unemployment rate.
Most illegals work for below minimum wage at jobs where the work would simply not be profitable at minimum wage. For example, a huge percentage of illegal aliens work as migrant laborers picking fruit. They need to move regularly to follow the work, they make only $15 a day or so, they work 12+ hour days, and they only work a few months out of the year. At minimum wage (in CA where the largest number of migrant laborers are), 12 hours work would cost the employer $90. When you factor in the costs of land, irrigation, planting, seeds, waste, transportation, marketting, etc, fruit farmers are only making pennies for every pound of fruit they sell. If it only costs you $15 to get 12 hours worth of fruit picked, it remains profitable, but barely. If you have to pay $90 to get that much fruit picked, it simply is no longer possible to compete with imported fruit from countries without minimum wage.
And, even if it were profitable, I honestly don't believe you'd find citizens willing to do that kind of brutal work, move every few days, live in shanties, for 2 months of minimum wage.
So, those jobs wouldn't exist in the US anymore without illegal immigrants. The fruit industry in the US would go out of business. And, when they did, we'd lose tons of legal jobs. The truck drivers, accountants, managers, marketers, executives, warehouse staff, secretaries, etc, etc, would all be looking for work. That's where the stat in the study I posted about losing 8.1 million jobs comes from. That's the number of people employed in industries that depend on illegal immigrant labor to remain profitable.
Also, many illegal aliens act as day laborers. If citizens wanted that work, they're free to line up with them now. Realistically most people that hire day laborers would probably hire the citizen before they'd hire an illegal. But even with the economy in the state it is, I have yet to see a single white guy standing out there with the day laborers looking for work... And I drive by two different day laborer corners pretty much every day. If citizens want these jobs, nothing is stopping them from taking them now. We don't want them.
I'll grant you all the costs for social programs and whatnot spent on illegal aliens would go down. I've heard an estimate that if you take the total spent on illegal aliens and subtract the sales and income taxes we collect from them directly, we're losing about $40 billion nationwide between state and federal supporting illegals. That's not a good thing, but it's a lot smaller cost than the impact to our economy of losing the cheap labor. IMO the solution is to figure out a way to get them paying taxes.
Fact: With no illegals there would be no murder, rape, theft etc etc commited by illegals. Which means those illegals that commit these types of crimes would not have been able to commit those crimes in the US. Which means more civilians would be safer with no illegals around. And really...how do you put a price on a persons life or raped body?
Technically you're right that the total number of crimes would go down if all the illegals were gone. Of course, that would also be true if we got rid of all the left handed people or all the people who have owned poodles in their lives. Any group of people commit at least some crime.
But, all indications are that illegal aliens commit far fewer crimes per capita than citizens, excluding the obvious crime of breaking immigration law.
Immigration and crime - The Boston Globe
That doesn't necessarily directy refute your point, but it does put it in perspective.