Gender, to me, is both ambiguous and obviously fluid. Concepts of binary gender, whether defined as the capital-M Man who "wears the pants" in the current (sexist) Dockers ad campaign, or the Universal Woman that second-wave feminists liked to imagine, are fictions. Such concepts obscure the simple fact that, even within our strongly gender-binarized and patriarchal society, people express gender in an astonishingly large variety of ways. Socialize people as we might, we can never warp every last person into a pair of perfect complementary genders; there will always be those who escape, even if they are only very few in number. I think gender is best seen through the lense of the Vulcan philosophy - "infinite diversity in infinite combinations" - with the added thought that a person's gender cycles through a number of those combinations in the course of their life.
I understand the idea of women's spaces as sanctuaries from patriarchy - although, theoretically speaking, there's no total escape from patriarchy when everyone is socialized into a patriarchal society, not even in a crowd made exclusively of women (or indeed, exclusively of feminists, or feminist women, or your particular favorite ideological strain of feminist women). I like the idea of special spaces where patriarchy can be greatly reduced; it's when we remove the lens of the gender binary that the whole affair falls apart.
Gender-binary essentialism, when combined with a vested interest in one's own perceived/identified binary gender, seems something akin to nationalism: one artificially divides an abundant diversity of people into Group A and Group B, identifies and sides with the interests of one of the groups, and proceeds to generalize greatly about the (generally good) perceived attributes of one's own group and the (generally bad) perceived attributes of the other group. People caught in-between these supposedly irreconcilable categories - Arab-Americans, transgender/gender-variant and andro people, people managing to be simultaneously "us" and "them" or the supposedly impossible neither "us" nor "them" - are thrown to the winds, trampled on, declared dangerous or out of their minds, or made invisible, ignored. Thus, gender essentialism breeds transphobia: when one erects immutable categories of A and B, and someone shows up who was raised A but always felt more B, or considers themselves AB (or C, or null), one simply does not know what to do with this person. According to one's mental constructs, this person simply must be invalid, or else one's entire view on the matter must be reconsidered. Obviously, most people in most situations will be very loath to question their cherished views.
The MichFest policy fails and becomes transphobic because it gives credence to the very gender-binary categories that oppress women (or "womyn," if you will) in the first place, placing more importance in how someone was raised and socialized than how they have struggled to define themselves. By this system of thinking, transmen are to be regarded as women, transwomen to be regarded as men and genderqueer/andro etc. folks to be lumped back into whatever binary category they were raised as, because they still carry with them the "mana," so to speak, of their socialization. Never mind that they work consciously to fight against that socialization - their past overwhelms all conscious efforts they could possibly make.
In my mind, MichFest actually damages the status of people "born" women - or rather, assigned female at birth - by perpetuating and re-ingraining the binary categories of "male" and "female," justifying it by unscientific and irrational, outdated second-wave feminist dogma. That type of feminism had its time and place in history, but if we are really to break patriarchy, we need spaces that are shelters not just from patriarchy, but from the gender binary itself - the system that makes patriarchy possible. We are not simply what we are "born;" we actively perform gender, and together we can perform our way away from the gender slavery that binary thinking imposes.
In short, the MichFest organizers really need to read some Judith Butler.
