We round them up because it improves grazing for ranchers in the same areas.
To let nature cull means to let them starve to death. I don't understand
why people get so upset over a human killing a horse (as opposed to a cow, deer,
moose). Go watch a "wild" horse live it's whole life in a crowded
pen for a few days and maybe your opinion will change. Many countries eat horse
meat, just because americans don't doesn't make it wrong.