It is a question that I have not gotten one to answer yet.
Quality of life never enters into these discussions as we flood ourselves with endless millions of exotic foreigners from all over the globe.
Mass immigration without end, forever, the endless humanity pushers never give a number for when enough will be enough.
Personally, I thought that America was fantastic when it was at about 200 million.
I could not agree with you more. It makes me so sad to watch 70s and 80s movies (for example, old Clint Eastwood ones). I remember the empty roads in the movies, clean national, state, local parks, drinking unfiltered water from Yosemite Valley in the mid-80s, and so on.
Southern Arizona held out until the late 90s, and I was still drinking unfiltered water in various spots. Then, the illegal invasion began in earnest, and we the taxpayers could no longer even enter our public lands (literally, for example, Buenos Aires National Wildlife Refuge, Organ Pipe Cactus NM, other southwestern wonders). The watersheds became contaminated quite fast too.