Intra-family externalities, revisited

Rachel Soloveichik writes:

I completely agree [with my earlier post] that parents aren’t perfectly altruistic toward their children, and parents are happier when their children are better behaved rather than happy.  But if society shifts toward giving more power to children parents are much less likely to have children.  The small effect on children’s utility from more toys may be hugely outweighed by fewer children being born.  That’s probably part of the reason religious parents have more children, because they have a set of norms that justifying pushing their children to good behavior rather than being happy.

My question is where the limits lie, once we make this a moral question.  Say you could cut a deal with a fetus or would-be fetus.  You agree to raise a child, under the condition that it remain your slave for life. You also make sure that the life of that slave remains better than no life at all, although just barely.  Should we, as believers in the Pareto principle, approve of such deals?  I’ll say no, which is one reason why I don’t put much stock in Nozickian libertarian rights.  But I find this view difficult to defend.  After all, everyone is better off (forget about secondary consequences, if you wish to make the hypothetical example airtight).  Should we allow parents, or corporations, for that matter, to make such deals?  And would we need actual consent from the child-to-be, or is it enough to recognize that in expected value terms the child-to-be would likely prefer to be born, despite the onerous terms of the deal?

I suspect that yes, it is better for the deal to be made.  More happy people is a good thing, all other things equal.  But it is also better for the deal to be broken, ex post.  Some ways of treating people are just wrong, even if they were agreed to ex ante.

Oddly, perhaps libertarians should welcome this conclusion.  Arguably their ancestors consented to rule by the U.S. government when they moved to this country.  Or perhaps you offer a kind of implicit consent from your consumption of public goods or from your dealings with broader society, nearly all of which favors the idea of government power.  But libertarians still can object to their current treatment, no matter what explicit or implicit agreements were made in the past.

What if parents agreed to have kids, but only on the grounds that those kids would not freeze their social security benefits?