I think there are straight guys who do drag, but don't quote me on that.I always thought it was you could only do a form of drag (queens or kings) if you were in the LGBTetc community.
Really, RuPaul is just following the rhetoric these folks have been spewing for years - straight and cis people aren't allowed to be proud of their gender identity. Cis men are the devil incarnate and cis women aren't as real of women as trans women.
Do these angry people want to be... actually inclusive?!‽
Part of the issue, I'm guessing, is that back in the day, you had trans people, transvestites, drag queens, etc all lumped into one big catagory. It's probably why people think that it was a trans chick (when it was actually a drag queen) who started the riots at Stonewall -- back then, they didn't really make any distinction between them. Plus gender-bending was kind of a trend back in the 70s -- think of the whole "glam rock" scene.
I don't think though that you can do drag if you're a woman though. And if you identify as a woman, whether or cis or trans, well, then you're not really doing drag, you're just dressing up really really fancy. I don't know what Rupaul's stance is on FtM, but for MtF, it doesn't make sense to want to go on a drag show. Unless you're dressing up as a dude (do they ever have drag kings?)
Now I for one love Rupaul -- he always cracks me up, but he never struck me as the easiest person in the world to get along with. And I'm guessing he'd agree.