Sure, adoption markets basically already exist, why not make them legal?

Not only are wealthier people better candidates on average because they can provide for the material needs much better and will on average have a more suitable psychological profile (we can impose legal screening of adopters too, so they need to match other current criteria before they can legally buy on the adoption market if you feel uncomfortable with "anyone can buy"). It also provides incentives for people with desirable traits to breed, far more than just subsidising them having kids of their own.

I think I may not have gotten the point I was trying to make across - I don't think all harm is of the form "violation of property rights", I think the reason "property rights" are a thing we care about is because their violation is harmful.

Would you permit a market in infants?

An interesting question, but not one I've thought about. If what I've said above is tells you what you want to know, I'm not going to try discussing this here. Otherwise I will.

One of the standard topics in economic approaches to the law is to discuss the massive market failures caused by not permitting markets in infants; see for example, Landes and Richard Posner's "The Economics of the Baby Shortage". I thought their analysis pretty convincing.

1) How can you so easily predict others' level of distress if you don't feel much distress from that source in the first place?

Looking at other humans. Perhaps even humans in actually existing different cultures.

2) Don't forget about scale insensitivity. Don't forget that some scale insensitivity can be useful on non-astronomical scales, as it gives bounds to utility functions and throws a light on ethical injunctions.

This is a good counter point. I just think applying this principle selectively is too easy to game a metric, to put too much weight to it in preliminary discussion.

Testing would be a lot of work and potential corruption for comparatively little gain in nailing down the sig figs.

This is a situation in which "Speak for yourself!" would apply. In the weirdtopia where killing other people's children is criminal damage and such damages are calculated being able to prove higher value of said property would and should influence the amount of recompense they receive. For the same reason that Shane Warne could insure his finger for more than I could insure my finger an owner of an impressive child would be able to have that child evaluated and treated as a more valuable piece of property than an inferior child. They would aggressively and almost certainly successfully fight any attempt to make their child evaluated as a mediocre child.

The emotional investment a parent makes in their child must be huge, and the damages similarly so. It seems perfectly reasonable for a parent to say, "There's nothing available that I value more than I valued my child, consequently no sum of money will suffice to cover my damages. Whatever you give me it's still going to work out as a loss."

This is reasoning we may use now. But it does not apply in the spirit of the weirdtopia where we evaluate children only as property without moral value beyond that.

Downvoted for sarcasm. I was under the impression that (unsubtle forms of) sarcasm in non-humorous discussions are outlawed on LW, and that's very OK with me.

Downvoted for being a wet blanket and incorrect assumption of sarcasm. If it's ok to talk about the implications of legalizing infanticide then it is ok to follow the weirdtopia through and have fun with it. I adamantly refuse to take on a sombre tone just because people are talking about killing babies. My due diligence to the seriousness of babykilling with my expression of clear opposition - with that out of the way I am (and should be) free to join Konk and Jayson counterfactual wherein the actual logical implications related to killing other people's non-people infants are considered.

On a related note - of all the movies I was forced to endure and study in high school the only one I don't resent as a boring waste of my time is Gattaca!

Leaving aside the amusing notion of LW outlawing sarcasm, I'm curious about how you concluded that wedrifid's comment was (unsubtle) sarcasm.

(Just to be clear: I'm not contesting your freedom to downvote the comment for that reason or any other, including simply being irritated by people saying such things about children.)

Working from the assumption that slave-traders are in it for the money? Yeah. Slavery stops happening when it becomes more cost-effective to pay the workers directly, than to pay guards to coerce them.

The main use of slave labor is agriculture, because it's easy to have a large group within a single overseer's line of sight, and output is easy to measure. Child labor has historically succeeded there because of the low skill requirement, and because an individual child's lower productivity was matched by lower housing and food costs. If a child costs more to acquire than an adult - specifically if that difference in up-front costs outweighs the net present value of that slim productivity-per-upkeep-cost advantage - anyone who keeps using children for unpaid ag labor will simply be driven out of the market by competitors willing to do the math.

The app people worry about is sex. Police and prosecuting attorneys (in the US, at least) are already willing to resort to extremely dubious tactics to score a pedophile conviction; this would give them a legitimate audit trail to follow. Someone seeking to purchase a child for such purposes would not dare attract so much official attention... unless they were suicidally stupid, which is the sort of problem that solves itself.