I don't think it's sexism for a female person having an easier time writing for female characters because she herself is female. I'm a novelist and I write for female characters quite well, but it'd be ignorant of me to dismiss a female's critique on if I write them odd in any way because "wow we're NO different." 

Men and Women are equal, but they do have different body chemistries and different experiences based upon their physical sex which gives them a perspective that is inherently different from the other. 

However, I don't think that's what the thread is about. It's about whether someone is comfortable playing with a male who plays as a female, or vice versa. Honestly? Who cares. If someone is comfortable with that, cool. If they aren't, you can't guilt trip them or judge them into being comfortable. They cannot help it. It's how they see things, and at the end of the day, the role play guild is escapism. As long as they aren't being an ass about it, don't be an ass to them on what they do and do not enjoy. Roleplay with someone else.