If the post literally reads "MY DAUGHTER HAS AUTISM BECAUSE OF [X] VACCINE" then it's not that hard to refute with scientific literate.

What is much harder to police with a coherent set of guidelines is a facebook page where thousands of moms have each written "I got my child vaccinated and then they developed autism". When a new mom, with little sleep and little background in biological science, who is still on the fence about vaccines, see those thousand posts all together it paints a compelling narrative without ever really having contradicted science.