Anyway, sarasa_cat was discussing several problems with Tumblr, including the tendency for misinterpretation, wank or tangents to set off a long reblog chain, partially or wholly unrelated to the original post, and often removed from its context. And by the time the OP can reply to the initial wank and correct any misunderstandings, it's too late: the Discourse has taken on a life of its own.
I described those participating in such a thread as "discourse lemmings." (I was thinking especially of those who react to the posts at the bottom of the reblog chain rather than to the OP.)
A term I'd already forgotten, and it might come in handy, so, there. Free to use.