In itself the anger shouldn't be a surprise. We all knew that people in Boston are angry with the Church. But now it's manifested in odd ways.
First, people are angry that the Holy Father isn't coming to Boston. Not just disappointed: outraged! They feel that he should have come to Boston, because he could... he could... he could...
Well, what could he have done to calm this anger? I can't think of anything that he could say or do that would ease the sense of betrayal, frustration, and disillusion that so many people feel. One more apology? One more acknowledgment that Bad Things happened? That wouldn't heal the wounds; that would only confirm what we already know too well.
The raw anger, the hair-trigger sense of outrage, confirm my earlier belief that it would have been a terrible mistake for the Pope to visit Boston. His enemies are dedicated, organized, and energized; his allies are shaken, scattered, and nearly numb. It might have made for an ugly scene.
When you know that someone's itching to pick a fight, you have a couple of options. You can plunge right in, ready to start swinging. Or you can wait until he cools down a bit and you can talk rationally. I think the Pope made the right choice this time.