I was thinking of the old saying "comparing apples and oranges." Categories like "SUV drivers" (to which Carrol objected) and categories like "women" & "gay men & lesbians" are not of equal status politically, in that the latter have a history of oppression that has created the categories & made them socially painfully meaningful, out of which civil rights & liberation movements have grown, whereas the former don't. In other words, the former are empirically precise and yet politically vacuous categories, while the latter are empirically imprecise and yet politically necessary categories (i.e., necessary until oppressions that gave birth to them disappear).
To repeat, not all categories are created equal politically.
Yoshie