Political violence and moral relativism
Good point, Ace, and it ties into the overall tendency on the Left to view everything through the lens of political relationships. It's something they cultivate through academia, leaking from there into the popular culture they dominate so thoroughly.
The Left performs political calculations before it decides whether something is "right" or "wrong." (The result of these calculations is usually a mixture of both rightness and wrongness in some proportion, unless one of the Left's sworn domestic political enemies is involved, in which case Absolute Wrong is more likely to be the result, carried out to several decimal places.) This is how they come up with beliefs such as the fundamental inability for members of preferred minority groups to be "racists." Racism is a power relationship, something that can only emanate from the group with all the power and privileges, never from the disadvantaged parties.
A similar process is employed to justify, rationalize, or ignore left-wing violence, from the Weather Underground types glorified by Robert Redford in a very poorly-timed movie to the overstuffed mass graves of communism. I notice there are some people already seizing on the words and writing of the Tsarnaev brothers, particularly Scumbag the Younger, in an effort to romanticize them. These people aren't striving to justify the Boston Marathon bombings, exactly, but one gets the sense they would like to put the bombings a bit further in the rear-view mirror.
Whatever else we may learn about the Boston bombers, one thing is already clear: their sustained contact with the American university system didn't armor them against the siren song of Islamic radicalism. One reason for all these student visas is the belief that foreign students will carry American values back home with them, liberalizing their home countries. That strategy doesn't seem to be working out very well, which is no surprise, because academic culture isn't doing a very good job of Americanizing the native-born, either.