Some abuse their permits - but remember, a rancher using public land PAYS for it and is monitored. You don't like the results, blame the FS or BLM - but both the FS & BLM often screw the rancher without cause, too.
A room mate of mine from college once paid $100,000 for a grazing permit. The next year, he was running 10% of his allotment when he got a letter saying his allotment was cut in half. He pointed out he was only running 10%, so it wouldn't change what he was doing. The BLM replied, "We are cutting what people are RUNNING by 50%, not what they PAID FOR - so he ended up having paid $100,000 for about $5,000 in feed.
Another time, he spent $20,000 on water improvements on the permit, then had the permit revoked the next year. Sorry boy - the US government sure appreciates the $20K in improvements, but you'll never get ANY benefit from it!
This for a guy who normally clears around $15,000/year in profit.
Feral horses are not different from deer. An overpopulation in the absence of natural predators will destroy the land. The difference is that we don't issue horse permits for hunting...