There's more value placed on the life of a human child than on an animal. Even if you think of the horse as your child, it's still an animal.
It's how society works, and you should realize that while, ideally, every little girl or boy has loving parents and that cute, fat little pinto pony in his or her backyard, this isn't an ideal world.
It's a painful subject, I completely understand why a lot of people are against it, but that's the reality of life. And wouldn't you honestly rather there be regulated slaughter so that the horses don't feel any pain at all or would you rather have them carted off to Mexico where they die in a particularly agonizing, painful death?
Think on it for a bit.
And if you really think slaughter is bad, do you have a suggestion on where those unwanted horses should go?
I personally agree with jemmamalone on this one -- to me, I don't think it's any more "right" to kill a healthy animal just because it has no home than it would be to do that to a human. And I'm sorry, but I don't have kids yet so my horse (and 2 dogs) ARE my "kids", I don't care what anybody says to me or how anyone else wants to judge me on that.
However, Xoras is right about one thing -- without REGULATED slaughter in the US, they're being carted off to Mexico or Canada and treated VERY poorly on the way there and once there - nothing humane about it. So while I do not support slaughtering just because it's hard to find homes for the horses, if it's going to happen anyway, I would rather it happen in the U.S. under STRICT regulated laws and in a humane manner. Unfortunately, the last time these were legal in the U.S., there was nothing humane about most of them...so enforcing the laws would be the particularly hard part.
Sorry if anyone disagrees with me, it's kind of a sensitive subject for me, since my horse was a rescue...I'm SO glad no one decided to give up on her and send her off to slaughter - she's the most beautiful, loving mare I've ever met and SO willing to learn!! I'm glad she was given the second chance that many were not. I get really upset whenever I hear stories of horses being sent away to slaugher, esp. the ones who are young and had nothing wrong with them, just weren't wanted anymore or their owners weren't able to afford them. It's tough, I know people are practically GIVING horses away these days because they're too much money, but I believe that if you truly love someone or something, you'll find a way to take care of them or find a way to find a good home for them. I would personally never send my horse to slaughter.