Would a society made up of totally selfish human beings be worse than the society we have today? Could it even function? In last week's Inaugural James M. Buchanan Lecture, Deirdre McCloskey seemed to think that the obvious answers were No on both counts. A society that practiced no virtue other than Prudence would be a disaster.
I'm not so sure.
Here's the key point: Suppose you were totally selfish. What are you currently doing that isn't already in your narrow self-interest? Not stealing? You'd be risking years in jail for stuff that you could safely buy with a little work. Not lying? Hmm, ever hear of the Boy Who Cried Wolf? Not giving to charity? How much do you give as it is? Refuse to help a friend in need? Before you say "It's not my problem," you'd be well-advised to google the phrase Tit-for-Tat.
Frankly, your current behavior is probably very close to what Prudence alone recommends. Your subjective motivation may not be selfish, but you roughly "act as if" you were. And if we think in terms of the selfish gene rather than the selfish individual, apparent counter-examples like parenting fall naturally into place.
Now suppose we repeat this exercise for everyone alive: Holding constant other people's behavior, how would you change your behavior if you were totally selfish? If each person answers "I wouldn't," then the status quo and Absolute Prudence are compatible.
Of course, this is an over-simplification. There would be some differences. But it's hard to say whether the reign of Prudence would make the world a better or worse place to live. Yes, charity to strangers would probably vanish, but selfless charity is already a pittance. (And Robin Hanson points out that even the selfish rich might give to charity to signal their wealth!) Drivers would be less courteous, and strangers ruder to one another.
But on the other hand, a world of pure Prudence has obvious advantages. Imagine a world where NO ONE was willing to die for a cause - country, religion, ethnicity, whatever. To make soldiers risk death, they'd have to start awfully poor and be richly rewarded. That sounds like a recipe for world peace to me. Similarly, imagine a world where NO ONE would try to hurt another person out of envy or spite. A great many conflicts would vanish, for, as Inigo Montoya says in the Princess Bride, "There's not a lot of money in revenge."
Bottom line: A world of pure Prudence would be rough around the edges. But there's no reason to think it wouldn't work, and a lot of reason to think that it would be both safer and saner that the world we see today. "All you need is Love"? It would be prettier, but it's never going to happen. "All you need is Prudence," is the more realistic slogan for a better world, because it encourages people to do what they're inclined to do anyway.