You need to balance the (large but restricted to an individual) utility to the kid against the (small to each individual and spread out access many individuals) disutility to society.
That’s reason for Pigovian taxes, not outright bans. There are plenty of other things which have diffuse negative externalities, e.g. anything which causes air pollution, and we don’t just ban them all.
Except neither Acty nor anyone currently in politics is proposing Pigovian taxes. Also, since most of the would-be immigrants wouldn’t be able to afford them, this wouldn’t be an acceptable policy for the pro-immigration forces.
That’s reason for Pigovian taxes, not outright bans. There are plenty of other things which have diffuse negative externalities, e.g. anything which causes air pollution, and we don’t just ban them all.
Except neither Acty nor anyone currently in politics is proposing Pigovian taxes. Also, since most of the would-be immigrants wouldn’t be able to afford them, this wouldn’t be an acceptable policy for the pro-immigration forces.