Good post, except I disagree with your first point. I think when you say that "social life is a war" but qualify that it's a polite war, and a positive-sum war, I think you're stretching the analogy to the point of breaking.

In my opinion, I think economics is the better model, if you look at social interaction as a sort of market, and people are trading back and forth. People don't like the idea of sex being a commodity, but in a very important sense, it is. Friendships and family are also commodities in this way. Acting out of duty corresponds, as I see it, as investing in your relationships with other people. There's always disutility in acting out of duty, but it's an important part of any relationship.