It used to be that fringe opinions were expressed on street corners on literal soapboxes and never got much further unless they had a certain level of credence. Now with the likes of Twitter and Facebook, these individuals have a global stage to broadcast to where they'll find a massive audience regardless of how bizzare and unfounded they may be, thanks to the legitimizing effect of the "communities" around these ideas. In the hands of someone charismatic this can be dangerously destablizing to society, because it's the perfect recipe for cultivating a following that believes almost anything imaginable, including ideas which directly conflict with demonstrable reality.
I don't agree with some of the things the internet has collectively decided to clamp down on but I do think it makes sense to not give just anybody the grand stage and spotlight.