I find this extremely interesting. I'm a straight, white, paid up member of The Patriarchy - but this is the only forum of the several I frequent where opinions seem to largely coincide with my own, and people seem to me to be talking sense.
The problem with the whole "cis" thing is that it reifies something that has only actually been arrived at by elimination, and then proceeds on the assumption that that thing is actually "A Thing" that exists inside the consciousness of most people.
I never decided that I was "cisgender". I never decided that I have a "male gender identity". Neither, as far as I can tell, did most of the men I know. What actually happened was that I was born with a penis, and then OTHER people made that decision FOR me. I'm only "cisgender" by virtue of the fact that I'm not "transgender" - ie, the discomfort and falsehood I feel between the limitations of socially-determined male gender and who I "really am" (which everybody feels to some degree) have not become so extreme that I want to wear and dress or have SRS. It's got nothing to do with anything I ever declared or decided about my own identity.
And yet because we are (rightly) trying to work out what the fuck is going on to make people feel like they are transgender, we have retroatively invented this concept of "normal" gender identity to contrast it with, and assumed that everybody has it. And now apparently, lesbians who don't want to be imposed upon by people who are biologically male - whatever you want to call them - have to check their privilege because of it.
It's bonkers.