Any explanation on Anna's flight? Spoilers

I think it ties in with the religious theme of sacrifice. They're trying to repent for their sins by sacrificing an innocent (or,in many cultures, a virgin- which is pretty much the same thing). This ties in to the constant referencing of Jesus because he too was killed for the same reason- as the man in the mental asylum often repeats, "He was kind."

Slight irony is that, for a group of people (including all of the priests who are at the scene of the Anna's death!) who speak of Jesus so frequently, to push someone off a cliff would accomplish nothing. The vast majority of Christians believe that Jesus's crucifixion was the ultimate sacrifice, and that, in his death, their sins are forever accounted for.

This means that killing Anna was simply a desperate final attempt at saving society- a hopeless attempt that the more-religious knew would solve nothing. Anna's death, and the crowd's willingness to push her off the cliff, also shows how quickly they (again- this includes the priests!) turn away from religion when the physical world becomes difficult to live in.

This is just how I see it, of course.