I don't understand why Will Wilkinson finds this so surprising: children don't make you happy, even though society tells you it does. Surely, a great deal of our raising involves society tricking you into doing things that are not in your immediate self-interest. Similarly, I assume that contrary to the popular stereotype, men actually must do much better out of marriage than women do, because society expends so much energy on telling women that they cannot be happy unless they marry, and trying to make sure they can't be happy by stigmatizing women who don't. If women genuinely got more benefits out of marriage, we wouldn't have so many social institutions that punish them for failing to enter that happy state.
And the intuition is backed up by the research--married men are healthier and happier, while the effect is more ambiguous for women. Most of the "marriage bonus" comes from men.
It's probably also true that in a pure state of nature rape is fun, stolen food tastes just as sweet, and hitting other people in the head is a pleasurable activity. Luckily, we have a society that lies to us about these things--lies so long that it actually becomes true, which is why most of us don't enjoy watching rape scenes and excessively graphic violence.
Unlike Will, I'm not okay with the human race dying out in a single generation, so I'd say it's a noble lie. And II'm sure glad my mother didn't have access to the latest happiness research.