American is built on immigration, and nearly all of us are immigrants or very recent descendants of immigrants. How in the world has immigration harmed Americans?
Given the impact the economy has on people's lives, it's an understandable fear. There's plenty of evidence for this not being the case (and in fact evidence for the "brain drain" strategy having substantial positive impact), but getting people to let go of a fear typically requires more than just hard evidence that it's unfounded.
(There's a separate branch of that fear, that imagines immigrants to be a drain on public assistance programs, but there's plenty of evidence that that is not the case.)
(Also, as always, policy is complicated and no comment that fits on a page is going to capture all the nuance of it or facets of it.)
Immigrants are not killing Americans en masse nor taking the land by force.