Imaculata
Hero
That doesn't make them right. It doesn't mean the game wouldn't be better if we included the things that upset them.
I'm not religious myself, but I can totally understand how the inclusion of demons (especially named after those from real world religion), removes the blur between fantasy and reality for some religious folks, and drives them away from the game.
I've never been fond of demons in D&D. 3E re-added them, but now renamed. And I think that was the right way to go. They decided to appease D&D players eager to fight demons, while removing that troublesome real world connection.