Boston could not have been prevented by the Muslim community. Dhohar never really attended any mosques, and his older brother didn't share his ideas with anyone at the mosque. You'll recall the only witness accounts at the mosque of his being there state he was thrown out of one for yelling and distrusting the sermon. (It was a sermon on how we Muslims should act more like Marting Luther King Jr.) The leader, Imam Suhaib Webb, threw his full support behind the Boston police.
Again, we're talking about the American Muslim community, which doesn't tolerate Wahhabism. I've been to dozens of mosques in a number of states and have yet to see any Wahhabism. The American Muslim community is a patriotic bunch.