People are complicated, and have blind spots. Evil people you can spot a mile off, and you can protect yourself. Good people with blind spots are capable of great evil, because they simply do not see it.
What happens even in our own time is that inevitably our consciences are in part shaped by the culture we are born into. For most people, the culture provides the moral compass, which means they are unable to see when the culture itself has gone off the rails.
But some people are able to do it, some people do see sooner than do their neighbors. GOP was born precisely because Christians were fed up with the Whig party’s unwillingness to take a moral stand and formed a minority party in 1854. A decade later slavery was dead and gone at least in its overt and legal form. When Christians wake up and take a stand, things change. After the war, Christians went back to sleep and the old evils reasserted themselves for another couple of generations.
True indeed. Evil slumbers but always keeps one eye open.