Certainly, and analyses like these always ignore the fact that there are absolutely people (a majority?) who had horrifying childhoods and who don't end up mass murderers because of it. The truth is twofold: these people are absolutely responsible for their actions (as anyone should be, I personally think 18 is too high) but we can at the same time recognize that society's worst (and Breivik is undoubtedly in that category) do not necessarily choose to become the worst, and that the psychological conditions that make it seem like it's ok to kill people are not entirely within their control.

Incidents like these are a public health issue like any other: they point to broader deficits in societal attitudes towards medicine. Specifically in these cases it is the extreme stigmatization of mental illness in much of the Western world (for lack of a better term and not to say that it's nonexistent outside the West, just that I don't know) that makes it difficult for people to receive the care they want and need.