Were this anyone but Amy, who has a history of terrible impulsive choices in regards to her relationship with Rory, I might agree. The Oswin thing... um, people actually say that, all the time. I've heard the "phase" thing said by several of my friends, gay and straight, after they experimented with the opposite gender.
See, this whole thing is why I avoid sexism debates on the internet. Once someone pulls the sexism card, it's an absolute judgment that can apparently never be revoked or rethought. Unless you agree with the "person X is inarguably a sexist bigot deserving of nothing less than the torment of hell" argument, you simply can't win, and are usually declared a bigot yourself for defending such an apparently-terrible person.
This.
It's also why I try not to discuss politics here.