Immigration restrictionists assume a zero-sum math for workers: A job gain for a foreigner is a job loss for an American. By that logic every college graduate who enters the job market would be cause for mourning. But that's backward, given that skilled individuals create, not take away, jobs.
This doesn't mean abuse isn't happening. But the abuse doesn't detract from the fact that the tech industry wouldn't be so big in this country without H-1B.