Okay. I've just spent a while retyping this comment so it sounds less wanky, but please tell me that you understand that what you are practising is straight-up, unambiguous misogyny? Saying you can't POSSIBLY write about female protagonists, it just CANNOT BE DONE, so you'll be using them as side characters for your male characters if at all...even if you believe wholeheartedly that this is your only option (which I believe it isn't) can't you see that the result is active, complete sexism?

Going back to what you said originally: I would like to write about more female characters, myself, and every time I start a story I think to myself, "Would this story work the way I wanted it to if the main character were female instead of male?" I don't understand why 'male main character' is the starting point and 'female character' is a possible 'instead of'. Why not start with 'main character' and take it from there? Why not flip a coin before starting?