Actually in many states/localities, there were criminal penalties for beating or killing slaves.
So, along with the silly Simon LeGree caricature (as well as that stupid ass in “Django Unchained”) as 100% reality, these portrayals are really misleading, both about the people and the laws.
You mentioned pets, but in fact they were more like working animals, so indeed it would be plain stupid to abuse and kill them. Only really sick and stupid people would be beating their slaves to death at all chances. Ever hear of a plantation with 100% kill rate?
I never realized it was illegal to beat your slaves in places. Not that the law wasnt abused but modern Americans think the slaves were treated like Russian gulag prisoners or Japanese POWs in WWII.
It just isnt so, but the marxist race baiters need that believed.
Your comparison to workipnk farm animals sound on the mark. Farmers mostly don’t abuse them and are often fond of particular ones. Then again, no farm animal is as unruly as a human can be, and I can understand an African tribal warrior refusing to be put to work or often trying to escape, and that would have merited punishment. It could escalate from there. But the idea of owners just beating people for sport, people who they want to be happy enough to work hard, that just makes no sense at all.