Robert Wright, Sociobiology The Moral Animal
New York, 1994: ISBN 0679407731
Page 115

Life is full of cases where a slight expenditure on one person’s part can yield a larger saving on another person’s part. For example: holding open a door for the person walking behind you. A society in which everyone holds the door open for people behind them is a society in which everyone is better off (assuming none of us has an odd tendency to walk through doors in front of people). If you can create this sort of system of mutual consideration—a moral system—it’s worth the trouble from everyone”s point of view.

In this light, the argument for a utilitarian morality can be put concisely: widely practiced utilitarianism promises to make everyone better off; and so far as we can tell, that’s what everyone wants.

Mill followed the logic of non-zero-sumness (without using the term, or even being very explicit about the idea) to its logical conclusion. He wanted to maximize overall happiness; and the way to maximize it is for everyone to be thoroughly self-sacrificing. You shouldn’t hold doors open for people only if you can do so quite easily and thereby save them lots of trouble. You should hold doors open whenever the amount of trouble you save them is even infinitesimally greater than the trouble you take. You should, in short, go through life considering the welfare of everyone else exactly as important as your own welfare.