No cooperation with authority
The anarchist principle of no cooperation with authority states that once some body has claimed to be an authority, or usurped one of the powers normally associated with authority, there can be no further contact nor cooperation of any kind with that person. They must be shunned and all effort must be made to disrupt their cooperation with others who share beliefs that their action was righteous.
For instance, once someone has engaged in outing, an attempted power grab that assigns a label or name to a body of work or behaviour, there is no cooperation or discussion with them in a community that follows this principle. Both gays and trolls seem to share a particular repugnance for involuntary association of body with label or name, and punish it most severely: at the very least, with absolute refusal to cooperate further with those who engage in it. Applying this principle strictly also shields acts of vigilantiism:
Outing journalist sources is discourable and laws exist to protect the source of journalistic information. To "out" someone in these circumstances, whether the outer knows those circumstances or not, is to declare war on their entire faction, a war some take very seriously. For another example, consider the implications of ratting on the mafia - anyone who does this will have to change their entire identity since they are certain to be killed for this if they do not.
Obviously, the no cooperation principle builds on itself since an action taken to end the unrighteous act is itself one that must be concealed by the community, if it wishes to retain the power to protect itself. If there is no confusion with group entity concerns such as legality or precedent then there will also be no doubt that the community knows best when to do this, and knows when not to do it, and that it will not be drawn into a cycle of simple acts of revenge - which would themselves require an authority to end and thus end the autonomy of the anarchized group.