I don't mean to be contrarian but you could side with the bad guys(and be the antagonist) in older BG games.
This. You could kill the leader of a slave revolt and ensure that children are sold into slavery. You could poison the druid grove for a few extra coin. You could free an immortal lich to access a powerful ring. You could perform a live sacrifice a to Demon Lord to get the most powerful hammer in the game. You could make slaves explode just to see them explode, you could feed them to spiders. You could sell silver dragon eggs to yet another demon to get a powerful axe. And the options to create zombies and to summon a demon to kill everyone are right there in your spellbook. You could allow innocent civilians get fireballed just so you could keep a silver sword. You could either help an evil race of shark men thrive or let them die in agony (no good option on that quest). You could kill random gnomes all for the glory of Lloth. You could keep a child's soul entrapped in a gem for more power. You can walk around in armor made of human flesh and wear a helmet made from the skulls of the mage's parents. You could give into your urges and become a lamprey faced monster. You could betray your allies and become the new lord of murder. And this is in core game, not the EEs which gave even more evil options.
Hell, good parties side with an evil thieves guild and betray their drow patron.
I'm glad those options are in the game because they make the good actions meaningful. BG2 got it right -- have evil options but don't make it the point of the game, leave that for niche titles like tyranny. (and Larian's data and the sales numbers of Tyranny makes it clear that evil options are a niche)
