GAD, I'm still struggling with the word, not the concept of intersectionality of oppression. I suppose my concern is that if people struggle to grasp what the word means, it is more likely to lead to confusion, misunderstandings and (I know it makes me sound cynical) more opportunities for those who would seek to divide.
Also, I think there may be wires crossing on the idea of what or who is divisive. I agree that the faces and voices generally identified with "mainstream" feminism tend to be white, educated and middle class. I agree with your comment, "women from outside of those descriptors may dispute what the mainstream is saying," and their challenges are often rejected by that "mainstream."
But, imho, it is some of those "mainstream feminists" who generate divisiveness when insisting that sexism trumps other forms of oppression. This has the effect of denying the existence of privileges they do have (e.g. due to ethnicity, ability, class, etc.) and failing to recognise the impact of other forms of oppression on women who fall "outside the mainstream."
I'm remembering at the time of the OJ Simpson murder trials, there seemed to be the expectation from many feminists that African American women should view it as a sexist crime while civil rights advocates insisted they should see it as a set up by a racist criminal justice system. Similarly, I've found that some with in workers' rights movements insist that racism, sexism, heterosexism, etc. are just off-shoots of the greater evil that is the class system. They suggest it's not worth spending alot of time tackling these forms of oppression as after the revolution, they will just disappear (as if!) These are the sorts of things I had in mind when I mentioned unhelpful divisiveness.
I agree that, "you are being divisive" could be used as a means to silence those who challenge the exclusivity of mainstream feminism, but paradoxically, imho if mainstream feminists refuse to recognise the impact of other forms of oppression, then THAT is genuinely divisive.