The idea of social constructionism is fine, but I don't think people have noticed that you cannot turn around and then claim that those constructs are sacred essences that you cannot question. This has always been a tension in feminism and gay / lesbian studies, and is going to be even more intense in trans- studies. If gender and even sex are socially constructed, then what makes my own private socially constructed identity so sacrosanct, so essential?
This is no longer even about group identities, since each individual can define for themselves exactly what is going on with that individual identity. But if gender and desire are infinitely fluid, then they also become meaningless. Those old devils masculine and feminine are lurking there, because fluid only makes sense if there are pre-established categories there to refer to. Otherwise it would be "fluid between what?"
This theoretical incoherence is striking. How come nobody notices it?