Mass murder cannot be condoned in anyway, especially if the victims are innocents, apparently they were killed because they where on a summer camp organised by the Labour Party, who in his mind were responsible for the mass immigration in Norway.
Given that his main concern was the rise of Islam, one must ask shouldn't he have aimed his violence at the politicians also Islam? Personally I would say neither, because how he went about it was wrong in the extreme, but as it as been said before there are similar problems in this country.
In reflection though, some on this site will openly state that they understand the Taliban's actions in Afghanistan, because foreigners have invaded their land (note: at their politicians request), but they are not prepared to understand the concerns of some of their own people regarding our 'invaders'.