Every newspaper has correspondents who are perpetually angry. I'm not talking about the righteous indignation that any citizen can feel when confronted with an issue that requires fire in the belly.
Anger spurs action. It's a good thing. I'm talking about people who are angry allthe time. They are invariably men. There is frequently a bitter underlying cause. In my experience, they have come out on the losing side of a child custody issue. Some have mental health issues, or deeply closeted sexual identity issues.
Some see themselves as champions against injustices. They fixate on extreme causes, or latch on to any cause. Some become serial litigants in court, arguing over minutiae. They won't take no for an answer. Some run for local government (thankfully, always unsuccessfully). This is a generalisation, formed from my experiences as a reporter and editor.
People such as these sadden and scare me, because often they actually have a point. But something has clearly derailed in their lives. Their anger needs an outlet, to the point when any action against the system becomes righteous. I believe this is what it takes to become a bomber.
I admit postulating a link between an angry serial letter writer and someone who commits an act of terrorism is drawing a pretty long bow, but at the heart of both is constant anger and an out-of-proportion sense of injustice.
There are plenty of healthy, thinking people who are committed to causes because it feels good to give time to something bigger than just themselves. Some do it because they are personally affected. Others commit to the fight because it is the right thing to do. And yes, some have a bit of righteous anger, and step forward to help. I do not know how to solve the problems of the perpetually angry man. But I do believe, as in the case of the Boston bombings, there are always warning signs.