Mary Douglas, the anthropologist, might say that like any binary distinction, a "dichotic gender paradigm" (or whatever you'd like to call it) makes anything that falls outside of the two available categories taboo in either a negative or a positive way.

A frequently-used example of a positive taboo identity would be the Native American berdache. Some negative taboos in Western culture that spring from grey areas in binary thought are cousin marriage (marriageable or not marriageable?), eating cats or dogs (pet vs. food animal), and yes, bi-/trans-sexual/gender people as well as any other queer who does not fit the dominant gender paradigm.

I might say that there is not enough room or flexibility in a binary system of thought to attain any understanding of a continually defined and redefined, experientally negotiated reality.