Overall, in the long term, I believe immigration is a net positive for the United States. I know others have mentioned the benefits, so I don’t need to repeat them. There are short term costs as well. Immigrants can place a strain on public services, particularly local services and they can depress wages, usually for lower skilled workers but even among skilled workers thanks to H-1B immigrants. The United States as a whole is capable of absorbing a lot of immigrants without worrying too much about them overwhelming us culturally.
I’m not really sure where to draw the line. But, yeah, I imagine there’s a point where the immediate cost is a bit too much for people to stomach even if it’s beneficial in the long run.
You are correct that internal migration may demonstrate if there are any potential problems with wide open migration … and there is.
The immediate cases to look at are places like the Phoenix region where population influx has outstripped water resources, or the Sun Belt metropolitan regions that have had growth overwhelm the educational systems. The tools to limit the influx are limited but implemented where possible.
On a smaller scale gentrification comes to mind, with higher income folk moving in, driving housing prices up so much the analogous “natives” families there, for generations even, are driven out, the neighborhood losing its older shops and getting Whole Foods, Juice Rx, and the Pilates studio instead. I don’t blame the old time residents there wanting restrictions placed.
So yes there definitely can be too much internal immigration, and little recourse to it.
On this I would argue even the opposite: this country’s secret sauce has been its hodgepodge stew of cultures. None overwhelms but all have added depth and complexity to the overall dish. Not melted together but chunks of different flavors abutting in novel ways. That ever changing stew IS American culture and is why our culture has been our most successful product. I argue for high rates of immigration for many reasons, including informed self interest ones, but arguing for control over the rate is not necessarily racist or ignorant. (Even as racists exploit ignorance as they use immigration bogeymen to further racist goals.)