I don't mean this to be snarky, but this sounds like someone who has no family, no kids, never been in a serious relationship. Once you're committed to one or more other people, you're pretty much putting their interests ahead of yours most of the day. If my friends who are parents are to be trusted, their kids are their priority in every substantial decision they make.

Also, it's surprisingly cynical to say that people don't put their interests above society -- most of the people I know have taken on work and hobbies that don't maximize their personal gain, because they'd rather improve society somewhat.

I just don't think that's true. Some people scrupulously pay taxes, but others don't and push the line as hard as possible. There's real variation in people's willingness to 'defect' from the public good.