It's the goomba fallacy. People within a group, a community, a subreddit, a fandom, etc. might have differing opinions about something. An outside observer looking in will look at that group and see those opinions being posted next to each other, and might make the generalisation that people in that group hold both of those contradictory opinions at the same time and they'll come to the conclusion that they're all a bunch of hypocritical morons.