'Jobs Americans Won't Do'

This is a favorite catch-phrase of the open-borders crowd (and their Commandante Uno Bush) - immigrants are just trying to make a living doing jobs that Americans just won't do. The phrase conjures up an image of a nation of spoiled brats, unwilling to dirty their hands in uninspiring toil.
So what would be a good example of a job that an advanced society would collectively shun? How about plumbing - while laying pipe at a new construction site may be inoffesive enough, the kind of plumbing work that has gone on at my 4-score-year-old house takes a pretty strong stomach. Yet plumbers are almost without exception native-born. How do we get them to perform their foul duties? Well you know perfectly well how - we pay through the nose.
Plumbers generally have to be licensed and their ranks - at least in these parts - are strictly union. And so the plumbing profession relies on what economists refer to as 'barriers to entry' to keep out cheap labor. The licensing requirements ensure a certain minimum skill level for people to get paid for plumbing, as well as restrict the field of available plumbers. The result is that a job that would have to be on anyone's short list of ones you wouldn't want to do ends up being in fact a fairly desirable profession - that is in fact not all that easy to get into. Now I'm not proposing that we start licensing landscapers and short-order cooks for chrissake - just pointing out the obvious disingenuousness of the open-borders crowd.