I would love for an economist to weigh in, but . . .

A law professor will have to do, because I've really been waiting for someone to address this issue. I'm too busy to post much but I'll try to be in and out until graduation in May.

Can it possibly be right that illegal aliens are doing the "jobs Americans won't do," so that their presence is no competition for workers who are citizens?

I would have thought that, as a matter of basic economics, it makes little sense to talk about "jobs Xs won't do" (at least so long as X is a large and heterogeneous national group). Rather, there are only jobs Americans (or enough Americans) won't do for a certain amount of money. Raise the amount you're willing to pay, and more people will be willing to take that wage to do the job; at some price, that supply would be enough to satisfy the perceived demand for such workers.

Now perhaps "jobs Americans won't do" is shorthand for "jobs Americans won't do unless the wage is raised to a level at which the jobs wouldn't exist in any case, since they won't be cost-effective." (For instance, if current American citizens just won't pick fruit unless they're paid $20/hour, only currently illegal aliens are willing to pick fruit for less, and fruit picked at $20/hour in America won't be competitive with fruit imported from overseas, then it may be that no jobs in fruit-picking would realistically exist for the current American citizens.)

I think he's right. The debate is about wages and not about some "types" of manual labor being beneath or otherwise unsuitable for Americans. And I think he's right that if my American apples costs more than those from another country, I'm probably going for the cheaper ones. The point is that it's not just as simple as saying "They do jobs Americans won't do."