Interesting and useful post!

But on your last bullet, you seem to be conflating 'leadership' with 'people presenting the idea'. I'm not sure they are always the same thing: the 'leaders' of any group are quite often going to be there because they're good at forging consensus and/or because they have general social/personal skills that stop them appearing like cranks.

Take a fringe political party: I would guess that people promoting that party down the pub or in online comments on newspaper websites or whatever are more likely to be the sort of advocate you describe. But in all but the smallest fringe parties, you'd expect the actual leadership to have rather more political skill.