It's the "Human Problem"
Politics or religion, we Humans always take an idea, ethos, belief, whatever, and form an organization, a group around it...and that's when it, the
organization, goes to Hell
It's inevitable, the more power/money is involved, faster and worse it gets, Psychosis and paranoid mania drives leaders to suicide, wars, genocides, burning books...etc etc
Anything that is "
Not what THEY themselves can tolerate they must destroy, as it upsets the limited scope of what they can tolerate before their petty little world gets shaken"
Left, Right, Christianity, Islam, Paganism, whatever, doesn't matter, one guy can take it and make it work beautifully, and another can turn it into a horror because he will not open his horizons, cannot bend the knee to another, cannot give and take, cannot laugh at himself.
That, is real life. Judge 'em by their deeds, not what cloak they profess to wear. "By their fruits ye shall know them"
Now, as a DM I often use some pretty horrific storylines and characters, because Sherlock Holmes doesn't fight Aunty May who steals some flowers fromMary Jane's garden...Jesus didn't wrestle with Uncle Albert the grouchy relative...
heroes need to confront
vlliains. they need a "worthy adversary", and sometimes, just such an evil, heinous SOB, that dropping a napalm strike via a Meteor Swarm up his kazoo, is a Justifiably Fun Act!
Having said all that, I have more experience of spiritual evil than most unfortunately
D&D is a freakin' GAME, it is often a complex morality tale we tell each other. This is a GOOD THING (tm).
True "Evil" is utterly corrosive, it's about absolute nihilism, hatred and destruction of everything, that exists, egotistical, monomaniacal, sociopathic mass murder by
suggestion, anything decent: kindess, honour, love are anathema and hurtful to it
Nitwits who go on about it haven't got a damn clue, and should STFU because if they DO ever encounter it, they'll never be the same, self-righteous twerp ever again, I can assure you.