Why? You sure can't eat them whole.
I have to seriously doubt if there's a big market for "free range" horse meat. I'd tend to believe that the largest portion of the sales would be for domesticated horse, raised for slaughter, as are cows and pigs.
I can't see this as anything but an emotional wedge issue by the PETA folks....
Once you start differentiating between types of animals, where do you draw the line? I've eaten horse, and it's OK. I've never tried dog, but probably would if the opportunity presented itself and the offering looked tasty.
I understand those who don't want to eat horse, but don't believe that there's any moral or ethical reason that others shouldn't be allowed to.