I agree with Shrieking Banshee that asshole angels are overdone. It especially bugged me in the Supernatural series. If demons are truly supernaturally evil, then there should be true supernatural good.
It's been overdone because of certain ideology that HATES anything that smells of Christian values, and that's based on everything being subjective, even truth (my truth), this ideology needs to demolish the very human notion that evil does exist (even some Atheists would recognize somethings as Evil), because only then can it become dominant in a culture.
While anti-Christian sentiment does exist, I don't think it's inherent in the modern mixing of demons and angels. (And I say this as a practicing Christian.) Personally, I feel redemption and forgiveness are at the core of Christian values. For example, I enjoyed Good Omens more than The Omen which it was parodying -- and I think it even was closer to Christian values. The Omen tried to make it a good act to murder a toddler because of his birth - while Good Omens instead had forgiveness and redemption of the child.
In any case, D&D has *never* been Christian. From the start, it has gone with paganism/polytheism.
Which is why the Cleric (and latter the Paladin too) is modelled after a Christian warrior monk.
Yeah D&D was never Christian, Doesn't mean their pantheon ever worked, as far as I know most polytheist religions have it's demons and angels, clearly deliniated as Evil the first and Good the second. Some even call everything gods, Lesser gods and demigods and still mantain a clear delineation between good and evil. Care to try again?
Yep, redemption is at the core of Christianity, and it involves repentance, penance, forgiveness. You need to repent, renounce the Devil, make penence to earn forgiveness.
Like I said several posts ago, a Demon might become Good, by following that exact path above, and it should be a strugle to finally achieve forgiveness and stop being a Demon. Ergo you can't have Good Demons or Evil Angels.
Or let me put it in a different way, fallen Angels already have a name, we call them Demons, likewise good "demons" already have a name, we call them angels. It's basic Theology my dude.