Your questions are somewhat difficult to understand, but I'll do the best I can.
The very first thing to be aware of when it comes to overpopulation is the
pattern of population growth around the world. The sheer number of human beings on the planet isn't really the point (although, clearly, there must be
some point beyond which the Earth simply can't support any more people.)
From Wikipedia:
LinkQUOTE
The United Nations states that:
Almost all growth will take place in the less developed regions, where today’s 5.3 billion population of underdeveloped countries is expected to swell to 7.8 billion in 2050. By contrast, the population of the more developed regions will remain mostly unchanged, at 1.2 billion.
The point is that the United States, and the rest of the developed world, is probably not at its maxium carrying capacity, but that the much of the less developed world has probably already exceeded it. The real question isn't "What is the maximum population which can survive" but "What is the optimal population which can provide the best possible life for humanity."
The lesson to be learned is that the way to limit population growth is prosperity, education, advanced technology, and the emancipation of women.
So, I guess I both agree with some of what you say and disagree with some of it.
I don't worry about the USA reaching its limit of population. I don't worry much about the level of immigration into the USA. By comparison with the truly serious problems that Western Europe is having with its immigrants (mainly due to a complete failure to integrate these immigrants into society), the USA doesn't have much of a problem at all.
I think that, on the whole, immigration has done more good than bad for the United States. The current level seems OK to me, at least for the short term.