I also do think that his acts are a consequence of his sincere beliefs and feeling of being powerless and censored [0].

And this is where the issue of being insane gets shady. A person acts from their beliefs, and the question is: how deviant these beliefs must be before the person is deemed insane? Not only that, but you must also ask for the justification for the belief.

Believing you'll wake up in the morning when you go to sleep: sane. (Justification: no evidence to the contrary; for a healthy person.)

Voices telling a schizophrenic person to murder somebody: insane. (Because the justification isn't "real" to "normal" people).

Believing that your homeland is under silent invasion of Muslims, with the help of politicians [1]: unknown. There are arguments both ways.

Believing that massacre/violence is the only remaining for you to escape censorship [0] and be heard: unknown, but probably insane. He probably could have attained a larger audience and influence had he been a better writer, like "Fjordmann" [extreme right opinions, no history of violence]. (In other words, he blamed external circumstances ONLY, instead of also trying to find the fault within himself.)

[0] As a foreigner who has lived in Norway for 8 years now, I have probably a different view than most Norwegians. Immigration is a touchy topic here, and "censorship" in the media is real, but very subtle: Whenever somebody criticizes immigration policies, even if it's most obviously NOT directed against a particular group, they're often dismissed as "racists", putting the end to the discussion. (Pure ad-hominem argument.) It doesn't help that such labels often come from members of the 3 currently ruling parties. (And remember that ABB's goal was to inflict long-term damage to the future development of a prevalent currently ruling party - Arbeiderpartiet.)

So, censorship is present here, only that it's in the form of public bullying and ad-hominems. There's rarely somebody who'll risk being called "racist" two times in the public.

It's almost impossible to have a factual, objective debate about immigration here. A debate which is truly needed, see the next footnote.

[1] Norwegian media paint an extremely biased picture of (muslim/african) immigrants here, in that that immigrants are most often mentioned in negative context. Also, there's almost a class difference in crimes: east europeans are thieves, burglars, pickpockets; africans and muslims are murderers, robbers, rapists.

Then they write about how police has difficulties keeping them out of the country, and you only rarely get to read about immigrants that get deported because they are criminals (yes, it happens very much!). On the other hand, they write often about cases where decent (law-obiding, well-integrated) foreigners get deported because they broke the "buerocratic" immigration rules, or were "just" illegal immigrants.

The picture painted by the mainstream media could be summarized as such: "The government's immigration policy is to throw out decent, law-obiding foreignesr, and to protect the worst of criminals."

You rarely get to read about "immigrant success stories" in the mainstream media, even though most immigrants end up being "ordinary, boring (as in unexciting, average) people".

[2] Also, in recent issue of "Morgenbladet", there was an interview with a left-oriented person (forgot the name) who declared himself a communist. His theory is that the governments of the EU indeed do stimulate immigration from 3rd world countries, but the ulterior motive is to split the working class and lower labour costs. He is not against immigration, though, but for more cohesive society.

So, is he insane for believing that Europe is under muslim invasion / in silent war with them (one of the claims that he was deemed insane for)? I don't friggin' know.

Norwegian media bubble (Aftenposten, Dagbladet, VG) is a dangerous one. There are other newspapers, sure, but much lesser read.

To conclude with my last $.02 for what they're worth.. I'm far from being an expert in any of {sociology, psychology, media}, but in my eyes, ABB and his actions are by large the product of:

1. Norwegian mainstream media, i.e., their way of covering immigration issues,

2. The inability and/or unwillingness of politicians to have an orderly debate about immigration, not only with their citizens, but also between themselves. You know there's something wrong when those throwing "racist" labels (instead of arguments) win.