However, it seems to me that the writer makes a mistake by attempting to evaluate a political strategy as though it was an academic philosophy position. That is to say, he's likely right that "identity synthesis" is not completely intellectually rigorous; however, it was never intended to be, it was intended to be a pragmatic political strategy.
For example, "identity synthesis" was likely never intended to suggest that there is literally a set of shared experiences shared by literally every member of a given minority group. It is just meant to suggest that in general a given group more or less shares a set of experiences.
Similarly, "identity synthesis" most likely is not concerned with whether, from a philosophical perspective, it is possible for groups to have knowledge of experiences they haven't had. Rather it is concerned with the fact that in practice the majority does not prioritize experiences they do not share with minority groups.
in taking a pragmatic political stance and argue that it is not intellectually rigorous; when I don't think it was ever intended to be.
For example, I don't think the point of