To me at least, designating a cultist as the default bad guys is just as lazy if not quite as problematic.
To be sure, laziness is often the goal for me, not a pejorative. It's very useful to have a quick and easy way to communicate to the players "These are the bad guys. It's okay to kill then." Or, alternatively, "You don't have to pause the quest and have a moral quandary here, it's okay to move on with the main plot."
You can always use vermin or undead, too. But something with more tactics is often pleasing.