I don't think the blame for America's "over-population" can really be layed on the immigration situation. Illegal immigrants represent .04% of the American population (going off of the statistic of 12,000,000 illegals). So can the "over-population" problem really be largely contributed to the illegals? Perhaps we should look into the baby boomer culture we live in before pointing fingers.
All of this aside, do we really have an "over-population" problem? We are roughly 5 times the size of India, yet they have a population of over a billion. We are geographically a larger nation than China as well and their population is over 1.3 billion people. Looking at the statistics, I wouldn't say we have much room to complain.
Just to clarify, that would mean illegals are 4 percent of the population, not 0.04 percent.