I suspect that while dark triad traits are desirable to women, they aren't the only desirable traits. As you said, research shows that agreeableness and altruism also tend to be attractive, and conscientious and agreeable men tend to be better dancers, and thus more attractive. (quick google search) I suspect that there are multiple types of attractive men, or you can still possess all these traits.

Then again, it is important to know how the dark triad is measured to begin with. I am not sure if this is the actual test, but it looks legitimate. While saying disagree to all or most of the questions that measured lying and callousness, I still managed to score high on Machiavellianism and above average in Narcissism. (low on psychopathy) This also calls into question how "dark" some of these traits are, since outside of psychopathy, the other questions were related to self-esteem and a desire for influence, which isn't inherently evil, and can still coincide with agreeable and prosocial personalities.
http://www.okcupid.com/tests/the-dark-triad-test-1