The majority of pop. growth in the US is coming from immigration, predominantly illegal. Aside from illegal immigration, we have a fairly low birthrate, and in turn, a low pop. growth rate.
You nailed it. The demands on our resources, social services, environment, and economy are being strained by legal and illegal immigration. If the Left was so concerned about the environment they'd stop immigration. But multicultural nirvana trumps all other values and goals.
STOP IMMIGRATION NOW!!!!
The problem is, everyone wants to live/work in certain regions of the country. All of the sprawl is concentrated in a few key areas that have registered continual economic growth.
BTW: People should have as many children as they can afford. I was heartened on recent trips to Utah and South Carolina to see several families with five kids, sometimes more. This contrasts with New York and Calipornia where the only folks with more than two kids are immigrants from the Middle East or Latin America.