I just watched Nemesis, the Voyager episode that turned this cliche on its head. That the more human you look, the more civilized and less savage you are.
But in general, it's always the human-looking aliens who are kind and helpful and the less human-looking aliens who are violent and savage. For instance, think of some of the most aggressive races we've seen: The Nausicaans, the Shelliac, them Jem Hadar.
And who are the most victimized, the most sympathetic races, who make such good friends with the Federation? Betazoids, Bajorans, Vulcans, Ocampa, Talaxians, Trill. (Mostly light skinned) Humans with pointy ears, wrinkled noses, spots, hobbitlike facial hair or other minor differences.
And all the violent, deceptive races are more monstrous looking to us, and generally darker skinned, like the klingons, romulans, farengi, kazon.
Is this strictly a result of costume budget and the fact the majority of actors available are caucasian, or is this something subconscious on behalf of the writers, that more like humans = more moral. Is Star Trek guilty of the same kind of exoticism it argues against?
Even in Nemesis, we would not have successfully been brainwashed into siding with the Vori if we hadn't been programmed into us to assume the more human, lighter skinned looking race was more sympathetic.