Hard to conclude, I think, the guy is insane. The manifesto suggests a rationale that is both extreme and not uncommon. Or perhaps I mean, not unique. But it is clearly a terrorist act and rather senseless in its aim.
I tend to believe all physical attack (including self defense) is sign of insanity, but not the kind of insanity that is physiological defect. The manifesto seems to suggest there was no other choice for this person but to carry out an attack, and from what I gather, he does see it as a defense.
It seems like the time for dialogue and healing through deeper understanding is not possible for his position. His mind made up, his war underway. With that in mind, it makes it easy to discount his role in the policy decisions of Norway. Not because of the horror of his actions. That more or less is a given, but because he seemingly has no way of connecting to a position of compromise and negotiation. Perhaps I am mistaken about this, and it does not feel right to put words into his mouth. Though the manifesto does have a stated position and his actions seem to be culmination of what that manifest is aiming at.
As jarofthoughts was saying it is up to Norwegians to decide how the country moves forward, and to take back sense of security, confidence and freedom. A call to bravery is most honorable. And should there be bumps along the way, Norway must know that rest of the world provides support and offering of blessings to 'choose again.'