Self-censorship is a norm which always existed as a social behavior, even online. In a small geeky world of early days of Internet, when community of connected people was small and more homogeneous, it was easier to touch certain topics without receiving strong reactions, but it didn’t mean self-censorship did not exist. It just concerned different things and the worst that could happen was a ban on the forum or IRC channel. It’s still the case for unimportant people: no one cares what random Joe says online. Everyone expects that opinion leader conforms to the norms of society - hence all those crazy scientists are being ostracized for spreading nonsense outside their field of research.