Well,there goes the thread...
Religion is never a good thing to mess around with.Still...it seems some people don't understand that OP is talking about in-game religion,not real-life religion.
And honestly,I agree with OP.All races already have some sort of a "religion" in lore:Humans/Dwarves - The Light,Night Elves - Elune,Tauren - The Earthmother etc.
I see no harm in introducing more lore and quests involving for example Paladin's faith in The Holy Light.It would just provide more immersion and connection to their character for players who want it and expand the lore around the "religion" in WarCraft as well as provide players with possible cosmetic options for their character (for example) depending on their race (Draenei/Human differences in the worship of The Light).