Peaches, most commercial sites where these issues are discussed will delete/ban you for saying human beings can't change sex. I know from experience. This censorship gives proponents of trans ideology a totally distorted view of how many agree with them.
Mumsnet doesn't work that way. Any opinion can be expressed as long as you post within Talk Guidelines. TRAs tip up all the time. They are totally unprepared to defend their claims or justify their demands because up until now they've never had to. They're used to the banhammer eradicating any opposition. They expect it. They depend on it.
Upon challenge their arguments reveal the absence of intellectual rigour in their ideology. That's if they stay long enough to actually argue. Nearly all of them spontaneously combust, breaking Talk Guidelines, leading to a ban.
This is one of the only openly gender critical women's forum in the Anglophone world. And here are some figures obtained from MNHQ last August:
Number of people entering the MN site via the Feminist Chat topic:
June 2016: 15,000
June 2018: 177,000
That's a TWELVE-FOLD increase.
And that's just people entering the MN site directly into femchat. Lots of people enter Mumsnet via other routes like active talk, and then navigate to the feminism boards next.
Overall site visits in June 2018 compared to June 2016 showed an increase from 17M to 26M, which is a very healthy increase of 53%. But the impressive twelvefold increase in visitors going directly to feminism shows a significant change in behaviour.