When I first started riding years ago, the trainer at the barn would beat the owner's horses if they were "bad" or "needed to be taught a lesson." I mean, putting them in the stall with a chain over their nose, jerking away and beating them with a dressage whip. She wanted everyone to follow suit, and a lot of the people did, but I refused to. When we finally moved, we told several of the owners what had been going on and they promptly left the barn. This trainer went out of business completely not long after.
This kind of cruelty goes on still and it's horrible to think about. Even with all the wonderful information out there about training horses these days, people still find it okay to treat horses this way. It's inconcievable to me.