I do think that this is about retaining talented workers and bolstering our knowledge-centric economy. These people are motivated enough to come to the US and succeed, we should try to keep them.
Besides, one of the bases of capitalism is that in any trade both parties should gain. If a company wants to hire someone at salary $X that means the company expects to get $X+K value out of that person. Assuming the company bets right that means we are adding value to the American economy.
Unlike importing products from China, importing people comes with various externalities. Here's a recent example of what you can get:
http://news.bbc.co.uk/2/hi/africa/7461099.stm
or, by contrast:
http://www.iht.com/articles/2001/01/05/kuala.2.t.php
...unending political nightmares.
We are in a world-economy, this is part of the deal. I understand that I'm arguing for working 1) with people I can't understand, and 2) for less money. It's just how the game works.
edit: I despise doing The Wrong Thing (tm) because it looks good politically. Maybe that makes me a bad politician, but I work in software development, not politics. Let the politicians worry about politics.