Why do Mexicans come to the US?

So I get a sitemeter report every week of who visits my blog. I used to get a lot of hits for a post I made "Why do Mexicans come here?". I think my answer was the most definitive there is out there, and I think people should see my answer when they google the above. This is basically a repost to get those hits back.

Mexico has killed it's labor leaders for way too long. A strong union movement is necessary for the middle class. This has prevented the growth of a strong middle class - heck - hardly any at all. Of course a society as top heavy as Mexico's is going to tip over. Mexico is in chaos. They are losing their best workers to the US. A strong middle class would help with the crime situation there.

The US, on the other hand, has a strong a union core. It needs to be stronger to keep the current middle class, of course, but Jimmy Jr. isn't getting shot by Feds.

Mexicans have two choices, to have a labor rebellion where thousands died liked they did in the US in the 1930's, or jump the fence. Their government could allow a strong union movement to grow without the violence. Since that's doubtful, is political unrest in Mexico's future? Again?

I'd probably jump too.