I don't disagree with being cynical about social media, but community belief is the overwhelming mechanism by which fact is decided throughout history, including now.
A community can certainly have beliefs, doesn't make them true in a factual sense. Some things are "decided" by the majority opinion, like how we think of gender. Others have an objective truth, whether the majority likes it or not.
"Community belief", or the appearance of it, can be engineered by a bad actor with sufficient resources: an authoritarian state, a think-tank with sufficiently rich sponsors, or the platform itself.