how does femslash and slash parts of fandom compare on this issue? I know theres a few people who will argue that m/m slash is by definition by women. Maybe they are no longer surprised by others showing up from time to time but some do have an issue with it. Is this more common in slash fandom than femslash? If so, why might that be?

I can't speak for the m/m community but I've certainly never heard anyone argue that, say, a fic I wrote for femslash_minis wasn't femslash. Since I don't have your experiences in m/m (no one's argued that the fic I wrote for maleslashminis wasn't slash either, although I've only written a couple of m/m fics and a whole lot of femslash), I really can't compare or theorize.

i also wonder if to what degree the fandom might be more accepting of your presence because of your being known to hold radical feminist views, than another guy who writes similar fic but doesn't identify that way, or does but doesn't discuss it in their fannish journal?

Well, yeah. I mean, teh_no can have very anti-feminist views (and be a jerk besides) and people think less of him for it. Men in fandom do get judged, just as women in fandom will get judged, and the level of suspicion may even be that much higher (and I don't have a problem with that). But ultimately one gets judged on what one does and believes, not primarily on their gender (which can be hidden anyway).

The thing is, I'm assuming that all the males (and females) involved as formal interlocutors in the debates at fandebate are academic feminists (and so far, that seems to have been a safe assumption). So Will has the same tools as I do to establish cred, were he to want to do so.

And Will did mention his writing m/m slash in the debate, as having written slash.