We live in a time of identity politics, but perhaps this is nothing new. The citizens of the ancient Greek city states were proud enough of their separate identities to go to war, and the religious identities of the 17th century tore communities apart throughout Europe for almost a century. The only part of Foucault's writing that I agree with in large part is his writing on identity, but his focus was mainly on the power structures it created.
If I am interpreting him correctly, and he was always obscure, he thought that any identity automatically created an "other", an identity that was outside of the one adopted. These two aspects are intertwined as light and shadow; we cannot perceive one without the contrast of the other. This creates a space of exclusion, wherein one identity is validated and the other is repressed. He firmly did not believe that any identity was better or more valid in actuality than any other identity, but rather that we are caught in an endless play of identity creation and suppression. He had a grim take on the whole enterprise of a functioning human society that could move past these dichotomies.
However, Foucault was vague about his definitions of power, how identity actually constructs the dynamic, and how it is propagated through organizations through individuals. I don't think he actually knew. This vagueness has left his work open to endless interpretations, and unfortunately most of them are extremely simplistic. One of the worst examples, in my opinion, is the use of his work to fight against the established power structure by embracing identities as a weapon. As a trans-woman, I have come across these efforts frequently.
The idea is that minority groups, such as trans-women, are oppressed because of their identity, and the solution is to embrace for groups to embrace this identity and fight for its place at the power table. In doing so, these groups thus invalidate the oppressing group and turn the tables on the power paradigm. The problem with this, however, is that the paradigm hasn't changed at all, and the identities have become even more firmly locked into place. It creates more conflict and oppression, rather than progress.
And worst of all, to me, is that each of these identities is a way of dehumanizing another person. Placing the label of "trans" on someone and organizing society to punish this identity takes away the humanity, the person-hood, of a trans-person. But it also dehumanizes the oppressor, making all cis-gendered people less than human. They become trapped in a small piece of their humanity, and they rigidly defend it against that attacks from trans folk.
By playing into these identities, rather than side-stepping them and creating a new paradigm, identities that feel oppressed actually become the oppressor and keep the cycle going. A simplistic interpretation of what I am writing, and one that I hope to make clear that I disagree with, is that people of historically oppressed groups should not stand up for their rights. That is not in any way what I am saying. I believe that every person does have rights, not God given, but that we as humans have decided benefit each member of our species. I also believe these are human rights, not trans-rights or any other. Until we can embrace our humanity first, above more restrictive identities that bind us to conflict, we will always be stuck on the weary, endless cycle that the pessimistic Foucault predicted.