I can tell you right now. They don't have the answer to that. Some Anit-Slaughter activists can't see past the word "Slaughter" and they automatically think its horrible and wrong.
I do have an answer, I can't type it right now because it will involve thought. I don't think the idea of slaughter is horrible, I'm not a vegetarian.. I eat beef, veal, chicken, etc. However it is farm raised (at least to my knowledge, my dad buys a lot of it..) I'm sure some of the meat has been through a slaughter house, but my dad generally doesn't like to buy slaughter meat (unsanitary conditions).. I've said this before, I would be LESS against the slaughter system if it were done humanely. Actually if it were 100% humane, foolproof in terms of receiving the appropriate horses, etc. I might be indifferent. I would never engage in it, because IMO horses are pets/companions, just as dogs, cats, etc. are. We currently do not have dog slaughter houses (for food), the same for cats.
Eating animals for food is not horrible and wrong, torturing the animals instead of killing them kindly, humanely IS wrong. It is also inhumane to eat meat that has knowingly been contaminated with chemicals (I mentioned this in prior arguments, but dewormers, vaccines, etc.) that can put humans at risk. (even if the meat is being fed to animals, like dogs.. there is still a risk for humans for disease, by living in close quarters with a diseased animal)
So I would appreciate it if you didn't automatically jump to answer for me, there are actually plenty of thoughtful (if optimistic) ways that can be implemented to reduce the horse population. Actually, the horse industry will more or less be forced to comply with many of them since they no longer have a choice.
I will have an answer for you, Bubba13, but I can't type it up right now. (too much time/effort) I'll try to respond to you tonight or tomorrow night, as I'm off to train my filly. =]