As a matter of public policy, do we want to be a nation of 400 million by 2050, 1/4 of whom are Hispanic? Our current immigration policies pretty much guarantee that this will be the case. I have no doubt that we can support such a population with food, water, and shelter, but there are enormous resource implications if we want to maintain the same standard of living while becoming an aging country in much the same way as Europe.
Of course, the Dems need to counterbalance this trend by importing more people, but with the birthrate in places like Mexico and El Salvador plummetting, they will run out of people to import in about 20 years.
There will always be a supply of people who want to come to the US. Supply exceeds demand. Mexico's annual growth rate is 1.153% [compared to our 0.894%] and the median age is 25.6 years [compared to our 36.6 years]. The current fertility rate is 2.39. So the supply of Mexicans will still be available 20 years from now. El Salavador has an annual growth rate of 1.699% and its median age is 22 years. The current fertility rate is 3.09. So their future supply is even more plentiful. According to the 2000 Census, there are 9.2 million Mexican-born residents in the US and 825,000 from El Salvador.
I am not advocating global population controls. As countries become more developed and prosperous, their populations will decline and stabilize. Most of Europe is experiencing declining populations. My concern is the long term impact of our legal immigration policies and the lack of control over our borders. A sizeable portion of the world's population wants to come here. However, we can't absorb those kinds of numbers without suffering serious consequences.
Population growth rates in the developing world will continue to fall, the key factor being urbanization. To put it simply for others on this thread, in a rural society, more kids = more hands to work the farm. Add the fact that the main forms of social activity in rural societies involve either planting crops or "planting one's own seed" and you can see why agrarian societies have higher birthrates.
With the global movement toward urban areas, and steady employmet in service and industry, it should be expected that population growth will continue to fall (as it has throughout Latin America and Asia, and, to a lesser extent the Middle East).
Your concerns would be valid if population growth were static. Trends in the developing world indicate otherwise. There is a good reason why the Maquiladoras in Mexico can increasingly only find women from the South to work in unskilled occupations.
I am not a religious man, but a man who believes that rational choice ultimately wins over the irrational over the long run in all societies. As such, I will continue to take the "population control freaks", whether bourgeois Orange County/Fairfax County types, or Eurotrash, with a grain of salt. In 20-30 years, there will be no surplus labor from Mexico, so all of those who have sand in their vagina about seeing all of those Campesinos from Puebla at the local mall should chill out.