I'm going to commit a bit of geek heresy now: Joss Whedon is not a hero of feminism. True, he challenges the dominant portrayal of women as weak and insipid caricatures who exist only to be dragged from one sexually-themed plot/characterization point to the next. But he does so with a portrayal of women as strong and aggressive caricatures who exist only to charge from one sexually-themed plot/characterization point to the next. A different fetish does not negate the act of fetishizing. Nor does the genuinely charming banter his women are provided with as they traipse from rape to heartache to seduction to willful-expression-of-aggressive-sexuality.
It's absolutely an improvement from the status quo, and I'll take what I can get. But it ain't saving the world one hot and tormented martial artist at a time.