Many people think children are good. I am one of them! I like children personally, and would wish to live in a world with more children. Beyond mere aesthetic externalities, having more people means more ideas. Kremer 1993 (the other one) connects this with technological growth, even historically, when Malthusian pressures make it ambiguous whether more people speeds up technological development (it could plausibly be the case that a richer people leads to more discoveries, and thus a higher population leading to a lower level of steady-state income outweighs simply having more people. Digressions in the first paragraph are poor form, however, so let’s get on with it). It should certainly be obvious that today, at least, we face no such Malthusian pressure, and every person has some chance of being a world-altering genius.
Abortion is therefore a textbook case of something with incredibly large negative externalities. It has concentrated benefits, but diffuse costs. It is possible that aborting a fetus allows the mother to have more children later on, but this does not seem to be empirically backed. This study estimates the loss from abortion at 440,000 births per year. The mother faces a cost for raising the child, but by aborting it, imposes a cost on others. Some abortions would not happen if everyone who benefited from the child to come was able to pay the mother not to kill the child, but this is obviously unfeasible. This does not regard the harms to the child, which I see as being of no consequence whatsoever, but many see as important. Thus, government action is in principle capable of improving outcomes.
When someone pollutes or emits carbon dioxide, they also impose a cost upon others. We would not say that the optimal amount of pollution is zero, however. Even if we did think this, we would be totally agnostic as to whether the best way of having zero pollution was through preventing emissions, or by undoing the emissions once done. Any sensible carbon tax would have to include tax credits for taking carbon dioxide out of the atmosphere, just as much as it might tax people for putting it in the atmosphere.
Thus, I propose that we extend the same line of thinking to abortion. We should tax abortions and abortifacients, and use it to fund abortion off-set credits. One could be concerned that there will be negative selection in terms of who gets an abortion — discouraging poor mothers from getting an abortion, while allowing prospective mothers from rich families to get one. Thus, we could tie taxes to income, or family wealth, in reflection of the greater harm.
There are doubtless insuperable practical obstacles to implementing the program as proposed. The point really isn’t that. I want us to recognize that externalities are externalities, and if we believe that government intervention can be welfare-enhancing, then we should treat all externalities as basically the same. Nothing is sacred — to regard some things as sacred is to necessarily cause harm.