[guywithahat]

I'm not sure they always are. Certainly employers/managers are pro-US tech workers because it gives them access to lower-cost talent, and many H1B's/immigrants are supportive of it because they want more people like them. This is a common complaint of Indian H1B's and something I've experienced myself, where, especially before the H1B fee, they would only seriously consider other Indians/people of their nationality.

If you go into the midwest though there's more animosity about being replaced by lower-wage foreign talent. In my experience when US-born engineers support immigration strongly it seems to be a holdout from their college years, and not something they picked up since starting their career.