Earlier quoted context omitted.
The system a convention uses of having volunteers watching for bad behavior is actually already similar to anarchist concepts of community self defense. Under an anarchist society, the folks tasked with handling these sorts of things would be volunteers elected by the community (in a con they're instead volunteers screened by the con committee). There would also be an expectation that, in public spaces, it's everyone…
I posted this already to a different question, but tell me: according to what you said, isnt the KKK a good example for this? It came from the community, was supported by the community, also they were very outspoken against (falsely accused) sexual harassment. Playing the devils advocate here, but I really would like to know why this is not an example of anarchy; of course answers like people will behave differently…
Anarchists are on the opposite end of the inclusion spectrum, even including the wrongdoer in the decision process for what the punishment is, when possible.