The alignment system is a roleplaying tool not a gameplay mechanic.
It's both. Protection from evil works because evil is a real force. Holy weapons do extra damage to demons because goodness is a real force that can be captured inside a holy avenger. To hold a holy avenger you need to adhere to a moral code. You need to be both lawful and good.
Selune grants me real powers to smite her enemies as long as I act in way she approves. Selune doesn't care if I disobey the law, neither does she judge me if I obey orders I disagree with. But she does care I do things like create zombies, make deals with devils or sell the slaves down the river for some extra gold.
And I like this. This is D&D. My BG2 chaotic good conjurer was never completely comfortable with forcing elementals to do her bidding but she always put the vampires in their graves, freed the slaves and slew the dragons.
I also liked DOS2. I helped Sebille murder the master *and* the mother tree. I don't know if those decisions were Chaotic Neutral, Chaotic Evil or even Chaotic good but a lot of good people died as part of that effort. But I don't want to play another game in Rivelon. Or Eora. Or Westeros. Or any place with a moral muddle. I want play in Faerun where gods are real, where evil is real and the lore that makes D&D, ya know, D&D is faithfully implemented.
