MORE OR LESS
The "ersatz survival” defense seems to acquit the Mexican couple who want to have a first child, despite the local birth rate being too high. If they go on to have a second child, they are merely replacing themselves, plural, so the same rationale applies; but what about a third, a fourth, or a fifth child? If my first child in some sense adds to my lifespan, and so does my second, then why not a third or fourth? Granted, none of this is literal life extension, but it’s close enough that it works in roughly the same way as a justification for procreative decisions. Would we really say that someone was wrong to take a miraculous pill that would add twenty or even forty years to their lifespan? At some point perhaps reproducers and life-extenders have gone too far: by adding two hundred years to your lifespan, for example, you use up more than your share of earth’s space and resources. By adding twenty children to the world, you likewise take more than your fair share. But it takes a lot of life-extension and reproducing before these judgments seem warranted.
It’s peculiar to say, of any given person, that she should not have another child. And equally odd to say that she must have another child. Shifting our attention from Mexico to Canada, where the birth rate in some provinces is lower than the ideal, imagine a couple who do not want to have any children. Jacob and Olivia wouldn’t be bad at nurturing and providing for a child, if they wound up with one by accident. On the Reproductive Idealist’s account, they’re doing the wrong thing if they have no children, because they’re not helping their province attain its ideal birth rate. Proponents of Idealism will observe that when the birth rate goes down, people can lose jobs. The Social Security system is put at risk. The elderly are under-supported. Despite all of that, it almost never seems appropriate to say that someone has an obligation to make a child.
The survival argument used to defend reproducers doesn’t carry over here, but other considerations do. Reproductive obligations, if they existed, would entail that people ought to do many other things: have sex with someone, or abstain, or use contraceptives; go through pregnancy and childbirth, or not. Because of their intimacy and scope, these are things it would be very odd to see as morally required.
Reproductive Idealism is far too simplistic. Upon reflection, we must conclude that there is a prerogative to have a child if you want one, and a prerogative to not have a child, if you don’t want one—in many, many circumstances. It can’t be true that, morally, we have to do whatever it takes to help our society attain its ideal birth rate.
That being said, it can’t be wrong for a society to send some message either encouraging or discouraging reproduction—a message more muted than "You must have a child!” or "You must not!” What kind of messages would be appropriate?