I read a weird twist on this today. This is the transphobe's merry-go-round...

"Sex-based rights feminists" don't want trans men doing feminism in a trans way.

Their reasons:

(a) Old-school boring transphobia: A trans man is a deluded woman who can't give valid feedback about feminism because "she" doesn't recognize basic facts about sex/gender.

or

(b) New-fangled self-contradictory transphobia: A man shouldn't have the moral right to talk about his own uterus because a uterus is definitionally a women's issue. They won't express it exactly like that—they'll say something more like men oughtn't make suggestions about how women should do feminism, but when you boil that down into its components, it reveals itself as trans men are men, and they are free to "talk," but they should talk to a wall, because if they try to have a real conversation with anyone else, they''ll affect feminist discourse, and men shouldn't affect feminist discourse, even if we define something about them as being woman/female.