Here are some thoughts that deliberately do not address class and capitalism. That's because another post will follow that does.
1. Intersectionality grew out of an oversight. Nay, a failure. Its roots can be found in the so-called New Social Movements of the late 60s and 1970s: feminism/women's liberation, anti-racism/black power, LGBT rights/queer politics. In the context of the USA, it was because the anti-Vietnam War movement and (mostly student-based) New Left replicated the traditional political dominance of white/male/straight. With a little bit of violence to national specificities, in Western Europe it was the failure of labour movements and the working-class based revolutionary politics of the communist parties and the far left to take such matters seriously. At least initially.
2. If anything, "established" radicalism and official socialism/communism were hostile. Labour movements in the 19th century and after the 2nd World War worked to exclude women from the workplace, and by extension install them in the home. Labour movements have an inglorious history of enforcing a colour bar.
3. A rocky road has been travelled. Yet, despite some outstanding battles yet to be won the route New Social Movements, or, Identity Politics, have plotted these last 40 years has seen important milestones reached and passed. Officially speaking, sexism, racism and homophobia are no longer acceptable. In Britain at least an inclusive, civic nationalism is the preferred, sanctified mode of Britishness. Think the London Olympics. Don't think UKIP and the Empire.
4. Racism, sexism, and homophobia have not gone away. They are, instead, more underground than they used to be. Hate crime and hate speech can call the full weight of the law down on a bigot's head. But the case remains that if you're a woman, if you're a member of an ethnic minority, if you're not straight and/or present as the gender you were not assigned since birth, you have to put up with the grind of discrimination, symbolic violence and, occasionally, actual violence. The vitalism of the 'new', third/fourth wave of feminism speaks of the continued salience of sexual discrimination, for example.
5. Social locations are always social relations. What is more, they are negative social relations. Society, or 'the social', will never forget your gendered, racialised, sexualised carcass. It will never let you forget it either. We are not cultural dopes though, we don't dance to the rhythm of abstract, rarified structures - even if it sometimes appears as if that is the case. The social context, the field of power, the frame of networked interactions - call it what you like - it always-already conditions our lived existences. They do not determine it.
6. Disadvantaged social locations are something that is "done" to groups of people. But at the same time, because they are social relations, they can be remade. Subjectification is not the same as subjugation. The commonality of experience among masses of people is a well for the formulation of common grievances, common outlooks, and common objectives. Identity is politicised, and from this basis collective action can (theoretically) proceed.
7. The question immediately arises 'whose experience is being collectivised?' Did the Black Panther Party or the black nationalism of Malcolm X speak of the historic experience of African-American women? Did 1970s 2nd wave feminism in its liberal, socialist and radical iterations take on board the historic experience of African-American women? The answer to both questions was no.
8. As social beings, each of us can be read as a foci of multiple social relations. Some of those relations can, for a number of historic, cultural and socio-structural reasons, work to place ascribed categories of people at a systematic disadvantage. It is possible for one to inhabit more than one of these disadvantaging, disempowering sets of relations. This is the starting point of intersectionality.
9. As disadvantaged social locations cut across one another, must identity politics become 'nominally essentialist' - that is assume certain identity properties and proceed from there without getting bogged down in border disputes vis straight vs lesbian feminism, white vs black feminism, trans-friendly vs cis-only feminism, etc.; disappear into fragmentation and privilege checks; or seek alliances?
10. Each avenue corresponds to established political and cultural ways of doing things. Nominal essentialism, the "speaking for" all women, all black and minority ethnicities, all LGBT people maps on to pressure groups lobbying/campaigning for legislative and institutional change, promoting tolerance through official channels, and shifting attitudes. When it is successful, which tends to be incremental, there is a political/cultural trickle down that can, generally speaking, improve the quality of (a) disadvantaged social relation(s).
11. Nominal essentialist renderings of oppression has also undergone heavy depoliticisation. Gay men, for example, are less a political category and more a marketing demographic: a postmodern lifestyle to be catered for by our consumerist cornucopia.
12. Fragmentation is the pathological outcome of identity politics. It is not the effect of intersectionality. It is its failure. Its root is not so much a purer, more radical form of identity politics (though it can assume such a guise), but rather a political bend toward recognising x, y, z social location (or combinations thereof) as equally valid points of view. It becomes pathological and fragmentary when it is disconnected from politics. Or, rather, becomes a project of individual self-presentation - a project that lends itself well to the emergent narcissistic self. Hence the possibility of politics are closed, leaving behind the emptiness of identity display.
13. As social beings consistently and continuously constituted (and constituting) by interacting, disadvantaging/oppressing social relations, these are not Berlin Walls cutting each other off from each other's experiences. We can empathise. We can put ourselves in each others shoes. Our ability to speak, to understand is founded on intersubjectivity. Hence the possibility of reconciling difference, of building an alliance between multiple positions continually produced by disadvantaging social relations is possible. Especially when the relations that disadvantage simultaneously advantage certain elites. Oppression fragments the oppressed. Oppression homogenises the oppressor.
14. On what basis can an alliance of the oppressed and disadvantaged be founded? A nice idea, or some free-floating project discursively stringing together different flags won't do it. And, in and of itself, the intersectional commonalities shared by women, minority ethnicities, and LGBT people have so far not forged lasting political projects that take all of them on board. Especially when a small number of traditionally oppressed people now find themselves on the advantaged side of the equation.
15. This is where capitalism and class come in.