Just saw this too. So if the argument is only 'transmen' can play 'transmen' (even the definition of this role is wonky in this case as the person Scarlett was due to play, Lois Jean Gill never described themselves as 'trans' - they've been historically-transed by the transjuggernaut) because Scarlett, as a female, 'doesn't fit the criteria'.
The logic follows, after protests online at her casting in that role, that only 'transmen' should play this part as they are the only ones who represent and can know what this role is about. And only they 'fit the criteria'.
So the logic has to therefore follow that trans actors must only play trans roles, because , say, if a transwoman plays the part of a female, that wouldn't be right as they can't represent a female because they don't have that lived experience and don't 'fit the criteria' - because they are trans?
A transman can never play a male role, because they don't have the lived experience of a male. Like Scarlett playing a supposed-transman, she doesn't 'fit the criteria'.
So either those who champion and celebrate Scarlett stepping aside from this role celebrate transpeople either only playing trans roles and no other role or, unsurprisingly, there seems to be a logic fail along the way here.