Quote from sle:
I rarely write outside of the options section, but this thread is so full of it that I had to chime in.
Given how much effort, money and time it takes to secure a visa for your worker (be it H1B, L1 or EB1), it's pretty clear that employers are doing it because they can't find qualified Americans. It's a fact, accept it and keep going. Also, while I can't vouch for other industries, in finance H1B workers are making top dollar, so there is no wage depreciation.
The H1B, as well as L1 and EB1 visas, are just a sign of a broader trend. If you walk into any good hedge fund (for example), you will find that at least 50% of people working there are either immigrants themselfs or are second generation Americans. Somehow, the trend is that they work harder, are better educated and are more interested in their work.
From my college years, I recall that Americans were a minority at any science course that was not required for pre-med. And we are talking of the Big H which supposedly collects the best of the best - I dread to think what the situation is like at the lesser-name schools. Even in medicine, my Mrs said that in her MD/PhD program, 6 out of 10 students were second-generation Americans. My own PhD program was "majority-owned" by Chineese, followed by Indians, with some sprinkles of Russians and Western-Europeans.
So, it seems that the real question is not how to prevent these people from coming here, it's how to get more of them to come here.