AnneC: Mainly I see categories as useful only as "shorthand", and then only along very particular vectors.

All thinking is done in shorthand - the brain can't actually contain a 1:1 map of the universe - but some hands are much shorter than others; and I quite agree that there's no point in trying to make someone match the average (or mere stereotype) of the female-human cluster if you already have access to more detailed information about her than that.

What you're objecting to isn't so much the shortcut, it seems to me, as the way-too-short, much-shorter-than-necessary cut. "Playing with spaceship Lego" isn't an atomically detailed description of you either, but it's more information than "female (human)".