He seems a bit confused.
But, in truth, the support for Stock is not coming from reactionaries. It is coming from, for example, feminists who, in the previous generation, argued vehemently for the autonomy of and respect for women that they believe is now threatened by the dismantling of the idea of gender.
It's the idea of sex which is under threat. Transactivists don't want to dismantle the idea of gender, they think it's more important than sex. Did he mean to write 'sex' there?
There is a case to be made against Stock’s contention. Perhaps biological sex doesn’t determine much of our behaviour and therefore doesn’t matter a great deal.
Again he seems to have misrepresented her standpoint. It's the fact that biological sex determines what sort of body we have which makes it important. He doesn't seem to have a clue what the feminist position is. It's gender ideology which says that personality has to 'match' the body.