I think it’s a way of farming status/clout. People who make fun of people who pose fringe ideas are rewarded with likes. People who shut down people on “the other side” are rewarded with likes. People can get likes by pushing the prominent ideology and kowtowing to that majority. It’s for their personal benefit, and being online removes the real-life downside of bullying or disagreeing with someone where you have to actually defend your ideas or deal with someone who is visibly upset by your actions. In conclusion, the upside of nitpicking is amplified by our tribal instincts, and the downside is muted by the nature of being online.