The left ignore the benefits of the free market, and pretend that there is a better system out there. They selfishly expect workers the developing world to respect the "right" of the Western middle class to high wages, as if magically other opportunities that don't involve competing with the Western middle class will arise.
The right want people to think that capitalism is magic, because they don't even want redistribution, which mainstream economists believe is something the market cannot do itself, and must be done by the government. The right want people to believe that all government intervention in the economy is equally bad, whether it is fixing the price of rent, providing medical services, or a negative income tax.
That said, I don't think H-1Bs are best used on average paid contractors. I know people earning a lot more money who missed out on the lottery. These people could have contributed a lot more to the economy.
EDIT: Added scare quotes around "right" in response to a comment.