But the sources are listed below on Wikipedia, not in lemmy.

Nothing stopped someone writing a bogus paper claiming an MMR vaccine causes autism. It being a paper likely gave it undue credit to people who were convinced by it, not that they read it..

Right and we also use lemmy, but we still weigh and judge what we read here or at least we should. And we should do the same for Wikipedia, even though I would argue that Wikipedia has higher epistemic standards than Lemmy. The point being, the openness of these platforms is a quality on its own. Wikipedia isn't perfect, but it is far from terrible.