But I’m thinking more that it’s that they’re human, and maybe humans on both sides aren’t all that great at holding themselves to that bar.

Oh, you’re absolutely right. Both sides absolutely think “I’m going God’s righteous work” and that the other side is simply “evil”. The hyper-partisanship has been crazy for some time on both sides. And then along comes a sociopath authoritarian (Trump) to just kick it all up to 11…