This is a weird policy for reddit.
But also, Jesse Singal (and Graham Linehan, linked elsewhere in this thread) are infamous in the trans community for spreading hateful disinformation and encouraging harassment brigades and then complaining about "cancel culture" whenever anyone criticizes them or they say something hateful enough to actually get banned from a platform.
We wary of "free speech advocates" who have an axe to grind against a specific set of marginalized people and view any criticism they get or moderation techniques employed against them as authoritarian.
This is a very strange claim. Just off the top of my head, this definition of "mainstream mathematics" would exclude, for instance, Gödel's more famous theorems, a good bit of Grothendieck, some of the Bourbaki collective, and a huge amount of work from rather high profile mathematicians working today.
I'm not usually one to poke fun at these things but my friends who study formal logic/model theory/category theory/homotopy type theory/etc. will be excited to learn that they are not in fact doing mathematics.
We wary of "free speech advocates" who have an axe to grind against a specific set of marginalized people and view any criticism they get or moderation techniques employed against them as authoritarian.