"Why do we tolerate the exploitation of child labor in acting..." 

I agree with the sentiment but movies, television and the stage would be pretty sad without child actors - no Annie, no Oliver, no Paper Moon... There are laws to protect them - AFAIK, they are pretty strict in California especially. I'm sure more could be done but ultimately, the parents bear a lot of the responsibility and some of them are more stage struck than the kids. Having said that, I don't know if suicide, drug abuse etc. are any more prevalent among child stars than their peers.

At any rate and at the other end of the spectrum, Dennis Hopper just checked out at 71. It's getting dangerous to even look at the news anymore.

"Democracy is a pathetic belief in the collective wisdom of individual ignorance." - H. L. Mencken