Let me qualify this by making clear that I'm a Marvel guy and I don't know much of the history of Starfire. Of course, now that history is pretty irrelevant, which is why the question came to me in the first place. I ask for reasons related to her character and the absurd fan reaction to her.
First, if she really is in the reboot what she appears to be: Somewhat of a morally ambiguous sexual hedonist who struggles with feelings of detachment and solitude. From a writing standpoint, what is it that makes her a hero? I understand before when she was supposedly in love with J. Todd (or whoever it was), but now she clearly has a different agenda. What is it that is holding her to the 'good' side?
Aside from the way she is written, there is the fact that those who hate the character are so vocal in their distain. It is clear to me that she must move units, otherwise she would have been redesigned. So for all of the 'Slutfire' haters out there, there seem to be plenty of guys (and gals) who love the look and the character. I would guess that much like Juggernaut fans, Starfire fans wouldn't care if she embraced the darkside. In fact, I would take it a step further and say that it might make her a more interesting character if she didn't have to play by the rules that are supposed to govern heroine behavior.
In a lot of ways Starfire and Voodoo remind me of '90s Bad Girl characters. They are not quite as over-the-top, hyper-sexualized, but they do seem to be out of place among the likes of Supergirl and WW. Perhaps it would be more fitting for her to take a 'heel turn'. She can still get her own time (the more popular baddies have shown they can carry a mini-series), she can give the haters a reason to not like her, and she can finally be free of the burdens of Robyn/Nightwing/Batman's shadow and the standards of female herodom.
So... I think Starfire should be a villain. Agree or disagree?