Why bother joining the Labour party?

Now that there is yet another chance to vote for a leader of the Labour party, if you are prepared to pay £25 next week, lots of my friends, none of them Labour supporters, are joining up. Their idea is to vote for the Corbyn ‘continuity candidate’, who seems to be Rebecca Long Bailey, thus ensuring, they think, continuous Conservative rule. As someone who is not a member of any political party, and is therefore eligible to join Labour, I am thinking of following suit; but something gives me pause. There is a real question whether the extremists in Labour are any worse than the moderates. The Corbynistas are, for sure, nasty, stupid, narrow and wrong. But that is visible to anyone aged over 25. They have not behaved worse over Brexit than they have over anything else. The Labour moderates, on the other hand, traditionally considered respectable, have been unprecedentedly disgraceful over Brexit.