Some parents are bad, therefore we should stop them being parents. The unstated premise is that we have a wise and benevolent government capable of doing this. I don’t think eugenic thought is as anachronistic as you suggest. I’m guessing most people think eugenics was largely confined to Nazi Germany, and are unaware of the nastiness that happened in the States and elsewhere under liberal democratic governments. We’re not racist like those Nazis: we have nothing to worry about.

There’s a pretty simple solution to population control: get rid of the programmes that let parents lay off costs on others. Then their decisions over number of children will be optimal. Any externalities would then be pecuniary only (one more person to bid up the price of resources, but also one more person to follow Julian Simon in working to take the sting out of scarcity).

I am reasonably sure he was trying to clarify what I meant by “efficiency” by reducing the issue to a ridiculous claim.

In that sense it was a valid criticism to raise – as I meant efficiency in terms of having an efficient market, but it was possible to take my post in a less flattering light maybe.