What does brag achieve?

In the NYTimes op pages, there is a piece called Messing With The Wrong City-about the marathon bombing. The piece is full of indignation and chest thumping.

I fully understand the outrage Boston's people feel. But without any clues to who committed the crimes, talk like that is empty. AND probably is giving the culprit(s) a guffaw.

Revenge is a dish best eaten cold.

The saboteurs are incompetent judging by their work. Trained terrorists could have killed dozens, even hundreds of people. So forget about organized guerrillas.