Chris Bertram analyzes it:
We may be, now, in the world that Cass Sunstein worried about, a world where people select themselves into groups which ramp up their more-or-less internally coherent belief systems into increasingly extreme forms by confirming to one another their perceived “truths” (about Islam, or Obama’s birth certificate, or whatever) and shutting out falsifying information. Put an unstable person or a person with a serious personality disorder into an environment like that and you have a formula for something very nasty happening somewhere, sooner or later. Horribly, that somewhere was Norway last Friday.
Anders Sandberg urges us to check our cognitive biases when calling Breivik insane and bin Laden an ideologue. Richard Landes (cited in Breivik's manifesto) tries, but doubles down, in some almost Malkin-worthy rhetoric, on blaming the other side:
All those people who, in the mid-aughts, like Cherie Blair and Jenny Tonge among so many, thought that Palestinian terror was an understandable response to their hopeless condition, for which Israeli was responsible, owe it to themselves to think: what did I to contribute to Breivik’s despair, with my insistence that anyone who sounded the alarm was an Islamophobe?
The Dish 