Historically, US actually was quite welcoming of immigration, including from Mexico. It tends to ebb and flow. I was taught by an economist that typically you open the flood gates when you want the labor, while restricting it when you don’t. To him, labor works just like goods in supply/demand curves. Flooding a market can drive down value of labor, etc., which can be bad for local workers. Obviously it’s a little more complex, but that’s the jist.
The trouble is, with globalization, one must wonder if that S/D curve is still valid. I imagine it is in some sectors, but in others, those jobs have been outsourced. If this is a bigger strain on demand, then it’s better to keep immigration on lock. That would at least help explain why it’s so hostile currently, but I’m just thinking out loud. I don’t necessarily agree with the economist approach.