At the very least, the argument that women have an inherent ability to write good erotica, where men do not, is flawed. The poor erotica one may find on the Internet is probably more a function of the amateur nature of fan fiction than the gender of the author. For me personally, I am always concerned that what I write will be respectful to women, gay women especially. I also hope, as I think most people do, that what I write will be enjoyable to people regardless of their gender. At a very base level, I do not believe either men or women write for others anyway.
Sex is something that every human being, regardless of preference, understands.
It is something that can take two characters into areas of intimacy that they would not be otherwise able to attain. My experience with the world of fan fiction has been unique and rewarding. I have made new friends and have definitely become a better writer, but there is more. I am gradually learning how to write erotica and what my own limits are in doing so. The first story I ever wrote contained a declaration of love, a kiss, and a fade to black.