One of the failings of the OP was to not provide an account of identity politics itself, which I think has caused some confusion. The way I mean the term might be understood as 'label politics': the idea that, on account of one's identity falling under a certain label, one either ought to act in some manner, or be acted toward in some manner.
Two examples. The first from an ad I saw, just this morning, for a bank. The ad was just a picture of young girls playing rugby, all smiles, with the words 'moving forward together' or some such. Here the idea is something like: 'look, we support women doing things not traditionally associated with women, look how progressive we are'. As if the mere imagery itself was progressive in itself. I'm probably being unfair to the bank, who probably helps sponsor the girls rugby league, so is going in some way to put their money where their labels are, as it were. Still, the point comes across I hope. It's the effort of identification that is meant to do the political work here.
Second example. This from someone else, who was - rightly - complaining about a bunch of liberals who could not comprehend why gays might support Trump. The liberal logic (of identity politics) was something like: they're gay, so how could they support Trump? The idea, once again, was that the label itself ought to have borne the work of politics alone. As if the mere fact of 'being gay' ought to proscribe a certain way of acting, or of being acted upon.
The important point to make though, is that
none of this means that either woman nor gays do not have political claims specific to them. It only means that they must be articulated in terms of addressing concrete
problems and specific injustices faced by each. To agrue against identity politics is
not to deny that there exists, or ought to exist, a 'politics of women', or a 'politics of homosexuality'. It turns instead on
how those politics are practised. If this distinction is not kept under firm eye, any critique of identity politics can morph into a critique or denial that, say, women or gays have any specific political standing at all. 'Identity politics' is not just
any kind of politics that has something to do with identity; it is a very specific use of identity.
@fdrake, this is a reply to your PM as well.