Breivik isn’t insane. He did everything right: he socialized with the neighbors enough to keep them from being suspicious, he managed to gather enough material to pull this off without raising suspicion, he did his homework and managed to produce a powerful bomb, and succeeded in bringing the weapons and ammo onto that island to pull of the massacre.
He really strikes me as a villain from a spy novel or something.
And the extremely sad/disturbing thing is, is that there are plenty of more people with the same ideology as him, who would hold him up as an example and try to carry on his work. It’s people like him that should be rounded up and locked away for a long, long time.