Do We Have a Duty to Breed?

Commenting on Tyler Cowen's post reporting on Hans Peter-Kohler's paper [pdf] on the the effect of children on subjective well-being, Ross Douthat (subbing for Andrew Sullivan) writes:

Europe seems to have this pretty well figured out. And I don't mean to be flip — the European “let's stop at one” approach to childbearing really is well-calculated to maximize a certain kind of parental well-being, narrowly defined. Of course, it's also calculated to seriously diminish the “subjective well-being” of all the second and third children who don't get conceived because their parents decided it wasn't worth the trouble. And while the theory that parents have children “either for the benefit of the firstborn or because they reason that if the first child made them happy, the second one will, too” may be true in many or even most cases, it also reflects a certain degree of deplorable solipsism. The chief reason parents should take on the trouble of conceiving and raising a child is that the child is a good in and of itself – one of the greatest goods there is, in fact, in any moral scheme worth considering – not because they think that it will make them or their already-existing offspring happier.

That bringing a child into existence is “one of the greatest goods there is” may be a truism in Ross's moral scheme, it somehow figures into none of the major moral philosophies in the history of moral philosophy, as far as I can tell. Does Ross think that the entire history of moral philosophy is not worth considering? That he is a moral innovator of the first order? I think he's just not making sense, and insulting low-breeders on the way.
First, you just can't “diminish the 'subjective well-being' of all the second and third children who don't get conceived because their parents decided it wasn't worth the trouble,” because it is a logical impossibility, an embarrassment to reason. Ross is saying that there exists a person who is harmed by the fact that it has not been made to exist. It refutes itself.
Second, setting aside the logically impossible theory of harms, what is Ross's moral scheme? We know this much: there is more than one thing that is objectively, non-instrumentally good, producing new human beings is one of them, and is one of the most valuable. Let's just suppose this is true. Now, it is possible to acknowledge that some things are objectively good without falling under an obligation to produce them. That a state of affairs is valuable is almost always a reason to bring it about, but it does not create a duty to do so. Does Ross think there is a general moral duty to maximize the quantity of such objective goods, like blushing babies? If so, why?
And even if we do have some such amazing duty, it appears that there are other goods in Ross's moral universe. Do we have similar duties to create beauty? Truth? Even if babies approach the summit of Ross's taxonomy of goodness, surely some quantity or combination of other goods outweighs the value of an additional baby. A life spent realizing one's potential, achieving one's valuable ambitions, say. Certainly Ross understands that pregnancy and motherhood often require the sacrifice of a woman's other ambitions, other values she could have brought to the world. Surely there are things, even inside this fantastic moral taxonomy, that men and women could do with their lives to compensate for their choice not to have children. Surely not all childless lives are deplorably solipsistic. Surely living a happy life is of some value and must weigh something. Would a mostly unhappy world swimming in billions upon billion of children really be better than ours? Ross seems to think so.
Anyway, I doubt Ross's deplorably thoughtless moral scheme (“the only kind worth considering”!) merits being taken even this seriously. What Ross seems to have offered us is a little bit of autobiography: he thinks he has some kind of duty to sire a big family. I don't mind that, and I'm sure the future mother of his future children will know what she's getting herself into. I do, however, mind the implication that those of us who believe our lives may produce more good by having just one child, or by having none, are spoiled monads who do too little of value to compensate the universe for our existence.