This is something I've had trouble with myself. Here are a couple of things I've thought about in recent times:
Identity politics is forever stuck in a loop of acknowledgement. In the 60s you can see that a big issue was to get white people to ACKNOWLEDGE that this thing called 'white privilege' exists. Identity politics now does not attempt to go further than that, but still 'grows' in its own dimension. For example, with the uprising in Ferguson you see social justice warriors on tumblr whining about 'white anarchists fetishizing riots.' Rather than look at uprisings as potential to fight against these terrible systems of oppression that you mention, the ideological tool that is identity politics just gives them a difficult-to-argue, intellectually lazy means to express their liberal politics. Since the internet is so big, this never has to end. There will ALWAYS be 'fucked up' people to feel self-righteous against.
The 'post-left' people I encounter still try to be aware of the way society privileges them, don't get me wrong. But to focus on it and fetishize it ultimately implies that one doesn't want to get rid of the shitty oppressive system, one just wants everyone to acknowledge that it exists.
Also: you may be critical of the 'one big identity' phenomenon, which is good. But identity politics yields to that type of thinking all the time. The "Ally" phenomenon is a good example of that. Realizing that one is privileged and therefore can't possibly understand anything about the experiences of one not privileged, said people work to be their 'allies:' meaning to support the cause uncritically.
This one, to me, is more insidious and intentionally terrible. Resistance and opposition always has a dominant narrative, usually institutionalized by an opposing party, non-profits, or NGO's. If one is to be an 'ally' to 'women' for example, one is basically uncritically adopting whatever popular narrative exists in those circles. If, in this case there are women who disagree with these institutionalized narratives, they are considered 'not feminists' or something like that. Rather than try to be 'ally' to a totally diverse range of perspectives (some of which are totally enemies to each other), it makes sense to work with people who you feel some kind of affinity with. Identity politics, I feel, inherently leads to this kind of thinking. One has to think hard about it to break free from it.