I have no problem with people who identify as "pegasisters". They're not evil if they do.
But if they trot around town about it, then I'm going to have some issues.
Yes, bronies started out as a "male" term, but now it no longer describes people themselves. It describes people being in a fandom called "the brony fandom".
So, women don't have to not use that term. There are female bronies who identify as female bronies or just bronies.
The real reason now to use "pegasisters" is to stand out. To say, "HEY, I'M A WOMAN, AND I LIKE THIS SHOW TOO." It's used to only signify female bronies. For example, the Brony Mate ad says, "FIND PEGASISTERS NOW".
Some are cocky about the term. They tell everyone to call them "pegasisters" and not "bronies" for some reason.
And that just makes you sound a little like Anita Sarkeesian.
crapiputmyopinonaboutanitasarkeesianintothisnoweveryonesgonnahateme
So yeah.