It's cognitive dissonance, and they're going with the norm.

But if you look at history progress has always been slow, most people didn't care about slavery, humans haven't changed, we are still the same, what lead us to partake, justify and ignore atrocities in the past is still part of humanity.

It takes time to change the world, at first it's hardest, but maybe the pace of change will accelerate.

We like to look back at the past in disgust, thinking we're better than past humans, not the case, we just live in a different time where we have already made progress on some things which is what leads us to look back at things that have changed and think we are somehow superior.