I made a post about this earlier on my own profile actually (albeit locked to just friends) and my take boils down to this: The whole premise of roleplay as a concept is embodying a character that doesn't necessarily align with who YOU are. I'm very open on my profile about being trans, but this is more to ward off people who are Weird About That from adding me than in the interest of transparency- Because whatever my gender is, it's really irrelevant to what we're writing.

If someone's the type of person that thinks only women can or should write women (vice versa with men), I think this speaks more to the kind of writer they are (and potentially their shortcomings as one).