Plantation owners were outnumbered by their slaves, sometimes by ratios of hundreds to one. It made sense to treat slaves fairly so as to minimize resentment which could flare into rebellion. I think most slave owners made an effort to create good feeling among their slaves.
Slavery was an abomination but the stereotype of Southern slave owner as a brutish, masochistic, cruel monster who crippled and blinded slaves for punishment is largely a Hollywood creation, based mostly on Alex Haley's Roots, a book that we now know is fiction.
The reality is a lot more complicated. Slaves were expensive. They needed to be healthy. They were fed, clothed, housed, and given health care. They were given time off to rest and recuperate. To celebrate holidays. While cruel slavemasters certainly existed, cruelty and fear often did not produce the quality of labor that rest, health, and contentment did. Many plantation owners understood this.