They even had the final insult heaped upon them from their owners and even the clergy who suggested they were genetically inferior. But American slaves were better mannered, more civil, and less inclined to commit a crime than their white owners. They were,on the whole, by most historical accounts, a very civil, obedient and law abiding people. They were far better citizens than their educated, well fed owners. Well, perhaps to a degree.
Fear certainly is a motivator.
And I do not think the average American criminal is much afraid of the law or society, today. Society is not their master. So I concede that fear will work, to a point. But only to a point. And it really wasn't fear that made the slaves into decent people.