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.
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.