It just doesn't seem in keeping with the idea of gender equality to name a person's actions according to their gender
The whole theory of colorblindness as it pertained to racism has been widely debunked, because it serves no one to pretend that race doesn't exist - it does, and people of color have been dealing with the consequences of being non-white for generations. White folks coming along and blithely claiming that "they don't see race" isn't just sweeping that problem under the rug, it's pretty insulting, because it's denying these people a huge part of their identity, their lens through which they view the world for better or worse. Race DOES exist. People who are not white are societally disadvantaged, whether we want to believe it or not, and until those issues are resolved then racial equality, while a nice ideal, cannot be a reality, no matter how enthusiastically you go around declaring you "don't see color". Right?
So I think the whole theory of gender equality meaning that you can no longer divide/classify by gender is equally disingenuous. The fact of the matter is that there IS a gap between genders, and cisgender men have been in power just as long as white people have, and everyone else is, for better or for worse, living with the consequences of not being a cisgender man. It helps no one to attempt to blithely wipe the gender slate clean. People who are not men are societally disadvantaged, whether we want to believe it or not, and until those issues are resolved then gender equality, while a nice ideal, cannot be a reality, no matter how militantly you go around declaring that feminism means you can't point out gender differences.
And for the record:
It's called mansplaining because it's a thing that men do to women. It's that sense of "Let me explain you a thing, because as a woman you couldn't possibly know it, but I, a man, despite no actual training in this area, know All Of The Things by virtue of being a man." If you're a woman, you're not mansplaining. You're just boring and officious.