Yeah, some people are stupid, no one doubts that, as least a dumb horse has an excuse. Some people are giving away infants, right? Sarcasm alert - not meant to belittle your point.
I refuse to have one because a horse is, as you said, dumb and they are fragile.
Here are the options for reducing the wild horse population.
Capturing and gelding 90% of the stallions. This will take a lot of time and money and it will only reduce the population over time.
Introduce predators such as wolves and mountain lions. Ever seem what a wolf pack can do? Not pretty. And then you will have the problem of what to do with the predators.
There is also hunting and leaving the meat to rot.
If you want to be truly cruel you can do nothing. Let the horses starve to death.
Or you can have small round ups and have the captured horses turned into hides and meat.
The last is the only logical solution.