Let's be honest and admit that everyone had a hope about who the Boston bomber would out to be. Conservatives hoped it would be some swarthy Middle Easterner, which would validate their belief that the existential threat from Islam is ongoing and that their preferred policies are the best way to deal with that threat. Liberals hoped it would be a Timothy McVeigh-like character, some radical right-winger or white supremacist, which would perhaps make us all think more broadly about terrorism and what the threats really are. The truth turned out to be … well, we don't really know yet. Assuming these two brothers are indeed the bombers, they're literally Caucasian, but they're also Muslim. Most importantly, as of yet we know absolutely nothing about what motivated them. Nothing. Keep that in mind.
But for many people, their motivations are of no concern; all that matters is their identity. The sentiment coming from a lot of people on the right today runs to, "See! See! Mooslems!!!" Some of them are using the suspects' identity as a reason why we shouldn't pass immigration reform, and the increasingly unhinged Glenn Beck is insisting even today that the government is protecting a Saudi man who was involved in the bombing, I guess because the Obama administration is in league with Al Qaeda or something. Whether this has anything to do with the receiver the CIA implanted in Beck's brain to exert its mind control over him through satellite transmissions could not be confirmed.
We should note that there are people on the right being restrained and responsible; not everyone is like the repellent Pamela Geller, already referring to the "Boston Jihad Bomber" (and no, I'm not going to link to her oozing pustule of a web site). But here is an editorial from the upcoming issue of the Weekly Standard titled "Civilization and Barbarism," in which William Kristol labors to remind his readers that in the world there is us, the civilized folk, and our enemies, the barbarians. He casts a wide net (barbarism can be apparently be found not only in terrorist attacks but also in Roe v. Wade), but it's a plea to simplify your thinking, to make sure that in matters of foreign or domestic policy the only question is who is Us and who is Them. Once you've established that and you know that Them aren't human at all but just barbarians, all the solutions become clear. The foreign barbarians must simply be crushed, in the most violent way possible (though it will not be Bill Kristol or his children with their lives at risk; they have people for that). As for the domestic barbarians who reside in the opposite party, well, we don't want to kill them, but you certainly wouldn't compromise with a barbarian, would you?
To this way of thinking, when you're dealing with barbarians, understanding their motivations just muddies your thinking and saps your will. Identity is all that matters. Maybe that's because it can be so hard to understand other people's motivations. For instance, I get how someone could become enraged over the death and suffering that have been the collateral consequences of all America's various foreign adventures. But I can't understand how a person could decide that blowing up a bunch of innocent people could possibly be a morally defensible or even practically effective response. Does the attacker in these kinds of cases say to themselves, "This is really going to make a difference"? It's hard to get inside their head in a way that makes any sense.
So it's easier to say, "They did it because that's just how those people are." It's an answer that means you don't have to ask any more questions.