Backchannels don't have rules.In some circumstances, it may be possible for institutions to restrict or formalize a backchannel, in which case, it is no longer a backchannel. The fiercer the attempts at prohibition, the more likely the conversation will move elsewhere, and become less visible to the prohibitors.
I do not argue that an unrestricted, free for all backchannel is a good thing in all circumstances, although it usually is, which is why approaching this issue with a negative mindset is an instant fail. The backchannel is civilized and moderated by the participants, who set the social norms - which are widely different on 4chan than on a PLoS article. Backchgannels have no rules, but they have conventions, leaders and an open and questioning culture. Engage.