Stallman was extreme, but practically speaking he has never had any power and never tried to gather any. His extremism is characterised by pedantically talking about the logical conclusions of actions and working strictly within and through the legal system to accomplish his goals.

That is a type of extremism that is very uncomfortable when it is used against something held personally important, but it is exactly the type of extremism that we want more of.

Organisers of extra-legal justice mobs are the sort of extremists we can generally do without.

I think that's fine though. Extremists exist to help the rest of us work out which shade of grey looks right to us.