Even in the "secret evil" scenario, the secret pretty much has to be some odious behavior, or they would generate very little drama or excitement (no worse than the 100 humans in that jail over there). Given how beauty is somewhat over-valued in human society, it almost has to be something like cannibalism or genocide complex for the evil to "stick".
A good try, but personally I am not feeling it. Cannibalism might be shocking when it is a familiar good race doing it (i.e. Dark Sun's cannibal halflings), but as bad races go, it is pretty par for the course. Also, as was pointed out to me several times, skinny and dextrous has kind of been done as well.
(Edit: Also, in regards to humanity: yes, it could describe them, but if we stopped there we would not rectify the imbalance in D&D races.)
Drow kind of already do the " kill your siblings " schtick as well.
The mating article has put me in mind for something else though... Perhaps they are the real humanoid equivalent of 3e's dragons, in the sense that they have a bizarre mating ability that lets them crossbreed with all sorts of creatures. Their sin is bestiality and an accompanying "progenitor of monsters" motif. The core race is exceedingly beautiful, but their mixed offspring are often ugly, bizarre, and freaks.
So fratricide is out but bestiality/monstecest is okay?
I never said fratricide was unacceptably bad. I said it has been done.
I never said fratricide was unacceptably bad. I said it has been done. Two entirely different things.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.