Julian Savulescu suggests extending the idea of paying drug addicts not to have children to everyone. At first the purpose is to avoid the eugenics feel of discouraging only one set of people from procreating, but then he reasons:
“The benefit of a policy of offering inducements to sterilisation is that it would select those who do not value, do not understand, do not want the role of parent. And it is precisely these people who are likely to be the worst parents.
Being a parent is, at best, a difficult job. Why not excuse those with the least motivation and determination? There are plenty of others willing to take their place. And the earth can only sustain a finite number of people.”
It’s of course true that if you penalize an activity, those to whom it is most expensive already will be the ones to quit. However:
- The existing costs of parenting already induce those who dislike parenting most not to parent. Adding another cost to parenting would just move the line where it becomes worthwhile to parent, not implement such selection. Justifying this requires an argument that the level of value at which people find parenting worthwhile is too low, not just a desire to encourage better parents to do a greater proportion of parenting in general.
- “Excuse those with the least motivation and determination”? We aren’t exactly pushing them to do it. Why presume they don’t excuse themselves at the appropriate point? This goes with the above point; the line where parenting seems worthwhile could be in the wrong place if parents were pushed for some reason to have too many children, but why think they misjudge?
- Why would there be plenty of others willing to take their places? Presumably those wanting to bear children will do so already or at least would not start at a 1:1 ratio on the news that others are not. Few factors influencing conception depend on the ambient birthrate.
- If others really were willing to ‘take their place’, the exit of poor parents from parenting wouldn’t be relevant to the total population and whether the planet can sustain it.
- Presumably the issue is how big a finite number of people the earth’s resources can support, and more importantly why and to what extent parents should be expected to misjudge.
- Smaller populations are not automatically better if you value human life at all. That parents are unlikely to account for the entire value of their potential child’s life is a strong reason to think that parents don’t have enough children. If that is the overwhelming externality, the line should be lower, and we would be better off paying people to have children.
Meteuphoric 
‘We aren’t exactly pushing them to do it’
In a way, we are (at least in the UK):
The Effect of Benefits on Single Motherhood in Europe – Libertad Gonzalez; Labour Economics, 2007, 14 (3), 393-412
‘The results suggest that benefit levels have a small but significant positive effect on the prevalence of single mothers. An increase in yearly benefits of 1,000 euros is estimated to increase the incidence of single mother families by about 2 percent.’
Thanks for the link to the Time article. I had no idea that such a program existed.
[T]he line where parenting seems worthwhile could be in the wrong place if parents were pushed for some reason to have too many children, but why think they misjudge?
The assumption is appears to be that the population of potential parents exists on a continuum where the the “worst” parents at some threshold self-select not to have children. Unfortunately, all evidence points to the exact opposite conclusion: our fertility patterns are already dysgenic. By measures of intelligence, earning power, education, and general got-it-togetherness, the best parents are more likely to limit their own fecudity, while the worst are more likely to let sh!t happen all the way to the delivery room.
It is precisely Project Prevention’s ability to narrowly target a population of bad parents that is it’s best feature.
It’s not the sort of thing you can change your mind about afterwards though. Lots of 18 year olds could make a descision they’ll regret.
“The existing costs of parenting already induce those who dislike parenting most not to parent.”
The problem is that choosing to have children is not always the same as choosing to be a parent. Many people not inclined to be parents end up having children not by their own choice.
Tangentially related is the idea I once read from an economist on population control. Every woman would be issues two credits. For each child she gave birth to she would have to redeem one credit. If she wanted more than two children, she would have to buy an additional credit from another woman. Conversely, she could sell her credits at the market rate.