I’ll add: I have worked with many amazing engineers on visas (in the US) from all over the world (and written letters supporting them). This was at a large company that aimed to pay at top of market, and could never quite get enough people. These engineers were not disadvantaging anyone IMO. In fact, I agree they probably created even more jobs by opening up new areas for the company that it then needed to hire for.

I have also seen much lower skill IT workers on visas (often via the big contractors) that were clearly pushing down wages and causing unemployment for US citizens.