if it gets reported in the first place which isn't always the case when threads become echo chambers on certain boards
but also -
It's not at all the same as Twitter. On Twitter I can choose whom to follow. So I don't follow transphobic twitter accounts. Simple.
Is mumsnet an echo chamber or not? Sort yourselves out!
Do you understand what an echo chamber is Wotcha? It's somewhere like Twitter where you can just block any opinions you don't want to hear, or where an algorithm decides which opinions you'll be presented with in the first place. MN is not like that and that's its strength.
If you disagree with what people are saying then just post and say so and explain why. It can be tough if you're a minority voice on a thread - I know, I've posted on vaping and smoking threads since 2013 and have frequently been in a minority of one - but if you have a decent argument beyond 'you're all so mean and transphobic', and you can back up your argument, then experience tells me you will at least be taken seriously and if people still don't agree with you they will have to put up decent arguments of their own or they will look like fools.
If all you have is appeals to female socialisation ('don't be mean') or vague insinuations of transphobia without ever providing examples then of course that won't go down well. The vast majority of us started out as 'trans allies' and continued way beyond the point where it ceased to make any sense, precisely because we were afraid of being mean or transphobic, or appearing to be. It should come as no surprise that we see straight through those tactics now.