> Brutalist architecture is functional first (but often beautiful, too).

Brutalism was at its core an ideological movement, its purpose to create buildings for the masses in the new socialist utopias. As such, it often explicitly rejected aesthetics as decadence, and sought directly to shock the bourgeoise.

Also, being ideological and utopian, its purported functionality was directed at utopian people, not actual people, which explains why these building often don't, in fact, feel all that functional. One clear shortcoming is that ugliness breed ugliness -- people are much more likely to take care of, and in general behave well, in a pretty environment than in an ugly one, aka. the broken window theory.