Interesting that you would view it that way. Your Celtic forbears from 1200 years ago would likely have had a different view of the Norsemen, and might have recognized the berserker elements present in Anders Behring Breivik's attack.
This translation from the Haraldskvæði saga describes Harald's berserkers:
I'll ask of the berserks, you tasters of blood,
Those intrepid heroes, how are they treated,
Those who wade out into battle?
Wolf-skinned they are called. In battle
They bear bloody shields.
Red with blood are their spears when they come to fight.
They form a closed group.
The prince in his wisdom puts trust in such men
Who hack through enemy shields.[4]
I'm sure the monks at Lindisfarne were terrorized in 793.
Alcuin, a Northumbrian scholar in Charlemagne's court at the time, wrote:
Never before has such terror appeared in Britain as we have now suffered from a pagan race. . . .The heathens poured out the blood of saints around the altar, and trampled on the bodies of saints in the temple of God, like dung in the streets.
Us northmen are a bloody lot, aren't we?