On the other hand, Apple actually killed a functionality that your phone originally came with and you paid for. There could be a class action lawsuit here.
Any sane judge would just toss that class action lawsuit out of the window, because there's a free fix and it's called iOS 7.
If FaceTime is so important for you, you should upgrade. Alternatively, if you absolutely can't stand iOS 7 you could just use Skype or Hangouts.
So there's a choice there and I don't see how your consumer rights might be violated. Whether iOS 7 is ugly or not is not up to courts to decide.