Paul Graham has written quite extensively of why some things are considered "threatening heresy", and other things mere eccentricity. Ultimately, he concludes that in order for something to be tabooed, it must be threatening to some group that is powerful enough to enforce the taboo, but not powerful enough that the can safely ignore what their critics say about them. Democracy is currently so entrenched in western civilization that it doesn't have to give a fuck if a few people here and there criticize it occasionally.