[quote=backstabbath].
Again, there's a difference between portraying the existence of racism in a fictional setting and in building a setting toward racist philosophies.
How about we have demons and devils who aren't evil too? Why can't we have a society of demons who don't live in the abyss and don't want to take anyone's souls? Must they be forever defined by Orcus? Having demons only be evil is so lazy and boring!
This is covered. Fiends and Celestials are creatures of elemental nature not mortal. It even states in the PHB in the section on Alignment that if a Fiend stopped being Evil it would stop being a Fiend.
Also, most, probably all, fiends were formerly mortals. They're just mortals that so consistent chose hatred, selfishness, violence, and destructive attitudes that it became their entire being. And it's not irreversible. It's just EXTREMELY unlikely that a soul that got so full of hate and poison would choose to even try to turn things around.
So, the moment a Fiend became something other than evil it would be come something else.
The most stand out point of this is where one of the Archdevils used to be a Celestial. She's not one anymore because she stopped being a pure expression of Good. She's now a fiend.
Similarly, a Fiend that stopped being Evil would become something else... perhaps a Fey or a Celestial... or perhaps even a mortal... that's a decent Tiefling origin that comes with a lot of interesting story baggage.
Basically... Being a celestial or fiend isn't a species... it's a metaphysical condition.
