Actually, it's illegal to allow a BLM mustang to be slaughtered. That's one of their stipulations to adoption, that you aren't supposed to sell the horse within the first year and it is not to be used as bucking stock or sent to slaughter. That's also why there are thousands of unadoptable culls standing around in holding pens all over the midwest, costing taxpayers money to feed hay every day.
I have a mustang, he's one of the best horses I've ever owned. I intend to always have at least one in my barn. I don't want to see them all wiped out, but they need to find a better way to manage their numbers. What they are doing now simply isn't working. There are too many being bred and not enough being adopted and since they can't send them to slaughter, there is a massive surplus that we, as taxpayers, are going to feed for decades until the animals die of old age or sickness. When you're feeding 10,000+ horses daily, that adds up to a lot of hay and a lot of money.
If I were in charge, I would go through and round them all up, cull the poorly conformed or nasty tempered animals and get rid of them through slaughter (yes, that may demonize me to some folks, but I am pro slaughter and mustangs are still horses). Then, turn the well conformed animals out onto the range, having roundups as often as necessary to cull more from the herds, including some of the younger stock, but also older broodmares and stallions too. Adopt the younger ones out and either sterilize and re-release or slaughter the excess. That way, the good stock is continuing to breed for good stock, there isn't a massive number standing in holding pens having to be fed every day, and there's still plenty available for those of us who actually are willing to adopt them and give them a good life.
I am willing to bet that my boy much prefers having good hoof care, medical care, and easy access to good forage and clean water constantly without having to travel for miles and miles.
And he still gets to play herd stallion without actually having to fight to the death