Example: Thomas Jefferson.
Most Helpful Guy
No, I can't see how a slave owner could possibly be a good person. That doesn't mean that Jefferson was stupid. He was still a smart, talented and interesting man. I would even believe that he truly meant to be good but you can't be a good man if you own other human beings as possession.
As an analogy, I would use Eric Clapton: Eric Clapton is an amazing guitarist. Unfortunately, he is also a horrible racist. He has said some absolutely disgusting and insane things about foreigners and other races on numerous occasions during his concerts. So is he a very skilled man and a great musician? Sure. But is he also an asshole? Yes, absolutely.2
Most Helpful Girl
I can only think of them as being a good person if maybe they bought slaves in order to then free them immediately. I do not think that anyone who thinks it's okay to treat a human being like a possession could be called a good person - perhaps they did good things, but ultimately, they're not a good person.2