PETA is not the same organization as the Humane Society. Further, from where I stand, PETA is much less influential than it was in the 90s. I don't know why everytime anyone raises concerns about animal welfare, people try to sort of change the subject by starting to blame PETA for everything. It's like... well, that's a really good analogy but it's very political so I shouldn't post it. The point is, rather than blaming a boogy man for making gullible people believe a certain way, it might be more helpful to treat those people as if their beliefs and feelings were real, and actually try to engage with them, even though some of them may seem unreasonable or uninformed. Ahem. Rant over.
I wish there were a good solution to this problem. But with lack of predators and horses reproducing so quickly, what else can you do but hard cull? At this point, there is no way you could get contraceptives to enough mares to make a difference. You need to cull first, THEN use contraceptives.
one thing you don't mention is getting more people to adopt. I think a lot of people who care about this issue don't realize that there isn't that big of a market for these horses. There is much more supply than demand. Maybe YOU could adopt one of these horses, or raise some money and group adopt one. But before you do, find out how much it costs to KEEP a horse, and then you might understand part of the problem. Still, life in a pen, for an animal that was born free, must be absolutely terrible.
I supported closing the US slaughterhouses, but now what has happened is that they have been replaced by slaughterhouses in Mexico and Canada, so these poor horses have to first endure a terrible journey and then the slaughtering process. I would absolutely support culling the poor specimens, those who would never be adopted, and using the meat to feed poor people or other animals. The animals in the wild would have much better lives if they weren't starving themselves by over-grazing their habitat.