The troll-type threads that keep popping up, along with the sub-threads that attempt to derail other threads, are a bit of a puzzle. What is their purpose?
Obviously some are meant to annoy or disrupt and don't seem to have any other point. Those point-scorers (they wish) are never going to have much effect apart from being minor irritants, and anyway they give other Mumsnet users heaps of opportunities to set out basic arguments and enlighten possible new readers.
But I think there is something else going on, at least some of the time. There was a recent really long thread that was a lot sadder, once you ignored the absurdly patronising tone of the OP. It seemed to be trying to do three things. First, explain how sad a so-called "trans child" must feel about being their actual biological sex to elicit sympathy. Second, to use debating points and arguments to convince others that not only is dysphoria an innate, born-with condition in every case but there is just one permanent cure in the form of transition which always works and can be the real deal, so if you're sympathetic to the sad child you must agree. Third, to deal with disagreement by characterising it and any counter-arguments as based on irrational hostility and bigotry.
(1) got sympathy - sorry you're feeling sad but the best treatment is help to deal with reality (2) of course got nowhere as it wasn't, and could not be, backed up by evidence and reasoned argument. That always happens and always will. Activists can't persuade others through reason and evidence and they do know that. That thread was full of repeated assertion and attempts at emotional manipulation. So I reckon the real purpose of the thread is (3), when the arguments fail to persuade people, to make out that it's all because the other side are hateful bigots.
What's really sad then is that it seems to be about coming on here to prove to themselves and their supporters that everyone hates them. After the demise of "no debate", since they can't win debates or acknowledge other perspectives or rights, maybe this is the new strategy, to evoke disagreement so as to pretend it's all "hate".