At the risk of conjuring a scarecrow, I truly wonder how long cultists will be an acceptable villain origin, considering that most groups labeled cults aren't chock full of zealots but of normal people deluded by charismatic con men with delusions of grandeur. Moreover, most of D&D's cultists are based on stereotypes and propaganda against pagan and "Satanic" groups mixed with good old fashioned witch hunts. Of brainwashed minions deluded by Satan into acts of debauchery and violence. Ya know, the same things mainstream media labeled US as for the first part of the game's lifetime!
Again, there is a world of difference between followers of Orcus and any real world religious group, but the idea of a group of righteous heroes going into a cult's hideout and slaying followers of a demon lord hell bent on spreading evil ain't that far removed from some people's reactions to Internet conspiracy theories or what Jack Chick thought about us.