"we need more women/blacks/latinos/indiginous/etc in (insert random field)." I just ask "why?". Then watch them stumble for a second, with a blank look, as they try to wrap their mind around that simple response. Thats what I love about this argument. Since there is no reason we "need" them, theres no way to answer it, and eventually they either get pissy and change the subject, or show their hand, and prove that it's a "want", and a baseless one at that.