One of the topics Landsburg tackles in More Sex is Safer Sex is the puzzle of self-control. Why do people on diets "lock their refrigerator doors"? Landsburg's answer: "a taste for self-control confers a reproductive advantange"; or to put it bluntly, "a locked refrigerator is a babe magnet."
When you snack at midnight, you get most of the benefits, but your spouse (who has good reasons to care about your health and appearance) shares many of the costs...
...Dieting alone won't do, because no matter how trim you are, the babes are smart enough to suspect you'll revert to your natural gluttony if they're unwise enough to marry you... But if the babes can see that you actually have a taste for self-control, they might be sufficiently reassured to take a chance on you.
I find this whole story baffling. Yes, if you're choosing between the following:
a mate with a big appetite who tries to fight it
a mate with a big appetite who doesn't try to fight it
you'd prefer the former. But it's far better to find a mate who simply doesn't have a big appetite to fight. Why wouldn't evolution select for that trait, instead of people at war with themselves? And obviously, such people exist. Indeed, if you were to predict the weight of people given their preferences, you'd expect that the thinnest would be those without big appetites, followed by those with big appetites balanced by self-control, followed by those with unrestrained big appetites.
If Landsburg's story doesn't pass muster, what does? It's not a full explanation, but I still like my cynical story that lamenting one's lack of self-control is an attempt to deflect punishment for parasitical behavior:
Why do so many people use the language of addiction? I guess it's partly sincere. I realize that I'm unusually self-satisfied; always have been. But it's also worth pointing out that there is a huge social desirability bias here. Part of the reason why people who spend a lot of time and money on socially disapproved behaviors say they "want to change" is that that's what they're supposed to say.
Think of it this way: A guy loses his wife and kids because he's a drunk. Suppose he sincerely prefers alcohol to his wife and kids. He still probably won't admit it, because people judge a sinner even more harshly if he is unrepentent. The drunk who says "I was such a fool!" gets some pity; the drunk who says "I like Jack Daniels better than my wife and kids" gets horrified looks. And either way, he can keep drinking.