I think your idea of what 'evil' is, is rather narrow and superficial...very cartoony.. Evil isn't about murdering people just because they're good and you don't like good. That would maybe be the case for a small group of people.. but not most.
People go down the path of 'evil' because it is enticing: there's promise of power, of riches, of getting to your goals faster..... everyone else be damned.
It is about manipulating betraying, backstabbing, deceiving , using and abusing people, be they good or evil, be they your best friend or foe so long as there is something to be gained.
It is about about cooperating with people so long as it furthers YOUR goal.
Or if you want a pragmatic character, it is about being ruthless, making the hard decision, like..idk killing a small group of innocent people to save the many.
D&D definitely also contain the kind of evil that murder good people just because they're good, but then we're talking like Cyricists and Malar worshippers and generally the kind of people (and typically more monsters than people) that are Philosophically Evil and committed to the cause of Evil as an objective philosophy. I think that's outside of the scope of the game
