Some of my ancestors owned slaves in the South. I don't think they were monsters or evil people.
Of course you don't.
And perhaps they weren't. But the system was. And to deny that a system that enslaved human beings was not monstrous or evil is, in my mind, as reprehensible as those who deny the holocaust.
Probably not. Not all Nazi party members were monsters or evil people either. But such is the ability of even decent people to do unspeakably evil things, especially when the culture is blind to it.