Re: Why did the League of Shadows want to destroy a peaceful city?
I think Gotham was already marked on the League of Shadows plans. It was unfullfilled job, no matter what. Bane clearly states in when he kills Dagget.
"Gotham’s reckoning. Come to end the borrowed time you’ve all been living on..."
A hero can be anyone. Even a man doing something as simple and reassuring as putting a coat around a young boy's shoulders to let him know that the world hadn't ended.