You're right. Mexico with a strong middle class would solve this mass migration problem. But time may run out for us before that happens. How much of their population has trooped north? Twenty five per cent? And meanwhile, Arab terrorists have figured out that America's back door is wide open. Not good.
Check out Mexican birth rates in the past ten years. They've seriously dropped (as they have in many other third world nations). I'm sure that much of that is from growing prosperity along the border and from capital sent back by Mexicans in the US. The Atzlan morons don't even realize yet that demographics has already turned against their fantasies. It is not Mexico that will swamp the US, but the US that will slowly swamp Mexico.