Reposting a comment I made elsewhere, earlier:

There is a fine line between identifying culprits and assuming some kind of communal, or joint, culpability. My conviction is that this line is drawn at the point where acknowledged leaders put these horrors into the official, legal/religious form of a fatwah. Once these homicidal thoughts cross from the pews to the pulpit, the entire community becomes responsible to take a position on what is being said.