The question of sanity or insanity is a moot point. Indeed there have been two assessments of Breivik, which have reached diametrically opposed conclusions.
There is little question that the vast majority of people act in a social manner, acknowledging the existence and rights of others. Such people largely accept the need for lawful behaviour, are able to establish personal relationships, accept responsibility, and naturally display empathy and compassion for others.
There are a small minority of humans, however, who have genuine and complex personality disorders. They do not see life and society as you or I would see them.
Are these people insane? I am no psychologist and I am thus unable to define insanity, or sanity for that matter. Nevertheless whatever term you use (and I appreciate there may be legal requirements to pigeon hole an individual for the sake of determining the manner of punishment) I would simply class them as evil. Was Hitler mad (insane) or evil? Certainly, in his own warped way, he achieved a great deal for himself and his cronies during the early part of the Nazi era and there may be some who would say he could not have achieved that if he had been insane. But evil and with compassion, he most certainly was.
I looked up this online:
Schizotypal Personality Disorder
Characterised by abnormal or bizarre ways of thinking, people with Schizotypal personality disorder will often isolate themselves from others. In some cases they may believe they have extra sensory powers or believe they can influence the world and make things happen. Some researchers believe Schizotypal personality disorder is a mild version of schizophrenia, but without full-blown psychosis.
- Sound familiar in this case?