The thing is that on the level of abstraction where 'religion' prompts someone to kill people, it really is rather facetious to consider Breivik any different.

As far as I'm concerned (and others too, judging by the downvotes), his concoction of 'Western-european culture', Christian or not, that led to his actions, is on the same level as this particular case.

Singling out 'religion' as somehow a differentiating factor is like trying to differentiate between Hitler's eradication of gypsies and homosexuals. It serves no purpose other than raising the suspicion that one particularly hates gypsies or homosexuals.