How is that narrow minded? One spouse - even if they are mentally ill - acts solely on their desires and doesn't bother to think about the other person. Addicts only care about their next fix. They don't care about the people they are hurting. We all have selfish tendencies. When unchecked they ruin every relationship we have. Marriage, bands, teams, etc... Act in your own interests at the expense of everyone else and those relationships go south. Besides, mental illness is a rare reason for divorce. It's typically arguments about money, one spouse cheating on the other or one spouse abusing the other or their children. I stand by what I said. The best marriages - and the best families, bands, sports teams, etc... - quit worrying about self and do what's best for the other people involved. When everyone in the relationship does that, everyone ends up fulfilled.
Did it ever occur to you that there is a difference between cognitive selfishness i.e. I, I, Me Me..... whatever and selfishness manifested in people who simply cannot control that urge because they are unable to? I think there is a huge difference. You can't just pigeon hole everything into a neat little box...and say selfishness is the reason for divorce...because it often isn't. With the greatest of respect...your argument, while containing some valid points, sounds by and large, like over simplified fundamentalist dogma to me.