You have no facts. You worry about BLM mustangs being shipped off to slaughter. You think horses will rival cattle as meat animals, although cattle are much better at turning grass into meat. You worry about horses being slaughtered in the US, but they are currently being trucked to Mexico and killed there.
In response, you have...what? That horsies are too smart to be used for food? Hint - they already are, horses that no one wants, picked up by kill buyers and trucked to Mexico and killed under horrible conditions. And you want them to KEEP being trucked to Mexico! Why? Are you nuts?
Besides...horses are not all that smart. I’ve got 3 in my backyard, and their intellect is underwhelming. Nice personalities, but not geniuses.
As far as cattle's efficiency at turning grass into beef.....a cow consumes less as it chews its cud but a horse forages on a wider variety of plant life. A cow requires continual grass growth which is why they are supplemented in the winter months with liquid molasses and mineral - a very expensive season for cattle ranchers. The horse's incisors allow it to eat the shorter grass longer into the winter, therefore requiring less supplementation.
If a horse is a pet that has to be euthanized it isn't going to Mexico to be slaughtered as the euthanasia process would preclude it from being used for consumption, either by humans or to be used in dog food. That leaves us with abusers - a problem more widespread and manageable vs. the BLM's roundup and ship out. The horses the BLM are rounding up and shipping out are as a result of cattle ranchers using BLM land to graze cattle. It cuts costs for the cattle rancher to rotate to BLM land than it is to continually fortify pastureland.
I'm sorry to hear your horses aren't intelligent....perhaps it's their breeding or perhaps it's the person trying to work with them. It's impossible for me to know since 'I know nothing about horses'.