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.
-The Sheliak are highly territorial and consider humans inferior, but in their one and only appearance, nothing about them said they were aggressive (i.e. invading other systems).
-The Ferengi have under gone such a character shift that the ones seen in the first few seasons have virtually nothing in common with Quark and ones who come after him.
-The Talaxians certainly look nothing like humans.
-The Jem'Hadar only do the dirty work of the much more human-looking Vorta. And while individual Jem'Hadar have been shown to have some sense of honor, the Vorta (except for Weyoun-6) have typically been shown to be irredeemable.
-The non-Cabal Suliban in "Detained" were unjustly imprisoned by the Tandarans, whom the episode noted look a lot like humans.
-The Kazon were formerly enslaved by the Trabe, who proved to be untrustworthy in their own right.
-The Medusans were said to be so hideous as to drive someone mad, yet were supposedly a highly enlightened species.
-Most of the Triannon in "Chosen Realm" were religious extremists.
-We've seen unsavory individuals from the human looking aliens you mentioned: Betazoid Lon Suder was apparently a sociopath. Kai Winn, Jaro Essa, Colonel Day, Tahna Los, and Basso Tromac were unsympathetic Bajorans. Tanis was an unsympathetic Ocampa (so was Kes, for that matter, in "Fury"). We've seen deceptive Vulcans like Valeris and V'Las. Joran Dax was a murderous Trill.
Nerys Ghemor wrote:
It's interesting to note--and this does seem to add to your point--that even Tora Ziyal's appearance seems to change to fit the stereotype. The more we are encouraged to sympathize with her, the more the "Cardassianness" of her makeup is downplayed and the more her Bajoran features are emphasized.
We've seen sympathetic Cardassians: Daro, Marritza, Ghemor (the guy in your avatar), Natima Lang, Joret Dal, Gilora Rejal, Mila. Even Garak and Damar proved redeemable, despite doing some terrible things.