It does not logically follows at all. Nothing in what previous poster said prevents analysis of group behavior or treatment. It does not make it impossible to talk about race or gender or age - it only makes it less naive.
It makes it impossible to assign an individual identity — and evaluate individual behavior and status — as merely a function of their coarse-grained group membership.
It does not make it impossible at all. And it also does not need to. You can talk about how groups are influenced or how they interact without making all the interaction to be result of "merely" just that.
