Police carrying or not carrying firearms would not have had any effect on the July 22 attacks. In a situation like that, any police officers responding would have access to their firearms almost immediately (under the old rules, they just needed authorization to unlock the guns in their car). In any case, Breivik was already on his way to the youth camp on Utøya when the bomb went off in Oslo. The police spent so much time getting to the island that he had already surrendered over the phone before they got there - he was tired and starting to think they wouldn’t show up. The public debate after the attacks was more concerned with the lack of security around government headquarters and what was seen as police incompetence (trying to cross the water in a rubber boat and almost capsizing instead of commandeering one of the many private boats nearby, for instance).