Let me say first that I am well aware that American drones are blowing civilians to pieces in Afghanistan on a weekly basis, only we are not given graphic footage of the carnage so it is less real and newsworthy.
So what do we know about the bomber(s)?
It is pretty certain that they hated Americans. Hatred is what drives people who deliberately kill civilians - a total, all encompassing hatred that makes it OK to kill anyone who shares even a single characteristic of the thing that you hate, whether it be America as self-appointed world policeman or America as ruled by "liberals".
And this is the point. The top candidates for responsibility for the Boston outrage are (a) right wing hyperlibertarian anti-State "right-wing" extremists or (b) Islamists.
We do not yet know which it was, or whether it was some third group.
A terrorism expert considers right wing extremists to be the main candidate, on the grounds that it happened on Patriots Day, marking the beginning of the American Revolution, and in Boston, where the eponymous Tea Party (not to be confused with the cerebrally challenged modern organisation of the same name) began the process of Independence. It is also the day when taxes have to be handed in, and individualists hate taxes. The small size of the bombs makes them inconsistent with the Al-Qaeda approach.
On the other hand, plans for pressure cooker bombs exist on Islamist sites.
So we don't yet know. But the interesting thing is, both groups, right wingers and Islamists, see the American State as too liberal.
Right wingers just hate liberals.
Islamists hate America because its religion is not Islamic, because it allows women to go about showing their hair and ankles. Of course, there are other, politically focused objectives of Al Qaeda which nobody talks about.
There are differences. Islamists see the US Government as too hard on Islamists, right wingers see it as too soft.
What they have in common though, is hatred of the liberal quality of American society. That is why the best, indeed the only response of America to Boston is to react, as the Norwegians reacted to Breivik, with calm dignity rather than by shifting away from their liberal values.