There are all sorts of sources of pain. I think the wealthy more often have toxic family dynamics. And speaking from personal experience, those early feelings of social exclusion, of shame, are extremely hard to shake. I'm on the left and I care about everyone, so much it's painful to see the world the way it is.

Disregarding the false dichotomy, Anders Breivik, while definitely coming from an unusually troubled upbringing, seems to have a reasonable high IQ, enjoyed economic success, and have been able to at least mimic social relationships.

Addition: This weekend's mosque shooter in Norway is reportedly a 21 year old (NOK) millionaire. Fortunately, his antisocial behavior was finally corrected when he got a beatdown by a 65 year old. It would surely have been better for him and everyone else if he was more gently corrected and put on a better path long ago by family, friends, and society--someone tried to notify Norwegian security police but they didn't take it seriously, alas.