As an avowed natalist, I am certainly not going to object to
advocating for libertarians to have more kids. I would love
libertarians to have more kids. But as a strategy to promote political
change, it is problematic for the same reason as education and policy
activism: they are all public goods.
Having kids for your own personal happiness is, of course, a private
good. But that's not what Bryan is arguing here - he's got a whole
book coming out to do that. Strategic fertility is suggesting that
parents have extra kids in order to achieve long-run political change.
But just like educating, proselytizing, or advocating for good
policies, the costs of these extra kids are born by their parents,
while the benefits accrue to everyone. Thus they are a public good,
and will be underproduced.
Moving to a seastead may be hard, but at least the individual
immediately and individually gets the increased freedom. Making the
costs (in money, isolation, etc.) less than that increased freedom are
a major challenge. But at least we know that if we meet that
challenge, we can get liberty and grow a free society through
individual benefit, without having to convince large numbers of people
to engage in self-sacrifice for a distant vision.
This all sounds plausible, but I'm not convinced. Patri's point makes sense once viable seasteads are up and running. But there's every reason to expect a long, shaky start-up period where most seasteaders will make major sacrifices to live their ideals. And right now, research into seasteading is - you guessed it - funded by charity - including the tacit donations of talented people who give up much more lucrative positions elsewhere.
Patri's right that having more kids than you'd privately prefer is a public good. But it's much less of a public good than non-economists (and even many economists) calculate. Why? I doubt Patri would make this mistake, but most of the calculations of the "charitable contribution" of one extra kid either count the full out-of-pocket costs, or the out-of-pocket costs plus lost wages. That could easily add up to $500,000.
Fortunately, asking libertarians to have one more kid is much less demanding than asking for a $500,000 contribution, because people like their kids! It's more like asking them to pay $500,000 for an item they selfishly value at only $495,000, or $450,000, or $400,000. Imagine paying $100 for an elegant Cato banquet; the true charitable contribution, even by the IRS's calculation, might only be $20 or $30, because you get a private good in the bargain.
Bottom line: Almost any strategy for radical change asks people to voluntarily contribute to a public good. Tying libertarian change to private goods is smart marketing, but it's not enough. It's also vital to figure out how to get the most bang for your charitable buck. Maybe Patri's right that seasteading has a bigger expected return for liberty than strategic fertility, but he'll have to work harder to convince me.