Slaughter is not a pretty thing, no matter where it's legal at- and I do not support it.
If you ever watch a documentry (Not talking about HSUS, PETA or SHARK ones) just the one's for educational purposes, slaughter is a chaotic, and in humane way to euthenize a horse.
It really doesn't control the population or effect the horse market. The same amount of horses that were slaughtered in the US yearly, is about the same amount being shipped to Canada and Mexico yearly.
My belief, is that the only good thing about slaughter in the US is the fact that now horses won't have to travel as long through extreme climates.
Just thought I'd share, not trying to change anyones opinion or spark an argument since most of everyone is pro slaughter here.