James Taranto is laying the contempt on thick in his best Professor of Liberal Fascism manner -- "complete sophistry," "embarrassing philosophical error," "philosophical narcissism," etc, so you know he thinks he's got a Good One. His target, A. Barton Hinkle, made the crucial error of embarrassing Taranto, who had defended the proposition (not that he necessary thinks so himself! Read the fine print!) that the institution of marriage rather than any specific marriages would be harmed by gay marriage.
Hinkle rightly found this to be nonsense: "After all, you would not say a virus 'threatens humanity' if, in fact, no individual human person was ever harmed by the virus."
For his rejoinder, Taranto postulates a virus of his own:
The Hinkle virus is so fast-spreading that it soon infects every person alive, but it is largely benign. It has no effect on men, and only two effects on women: (1) it is passed on to any children they have, and (2) any children they conceive after infection will be born homosexual.
Blink. Blink.
The Hinkle virus would seem to fit its namesake's criterion that it does no harm to any individual human person. We have established as a condition of the experiment--and we trust that in the real world Hinkle agrees--that it is not harmful to a woman to give birth to a homosexual child, nor is it harmful to a child to be born homosexual. And since the virus affects the sexual orientation only of the yet-unborn, it should not disrupt any existing heterosexual relationship.
Yet it should be obvious that the Hinkle virus would threaten humanity by dramatically reducing the incentive to reproduce...
Taranto could as well have said "any children they conceive after infection will be born male" -- nothing wrong with being male, right? -- or "any children they conceive after infection will be born female" -- nothing wrong with being female, right? Which in the long run would have an even more dramatic effect on reproduction, if not on the "incentive to reproduce." We could use this, I suppose, as proof that masculinity presents a threat to mankind without blah blah. Or femininity!
But Taranto's point isn't really that "X may harm humanity without harming particular humans." It's more like You liberals think homosexuality is harmless, but what if everyone turned gay?
He follows this with reams of universals-vs.-particulars guff to retroactively class it up ("Humanity is not 'simply the sum of the humans in it' any more than A. Barton Hinkle is simply the sum of the cells in him, or those cells are the sum of the atoms in them"), but they don't relate to his virus analogy at all. They're just fancy cover for a dumb joke about gays -- such jokes being among the last pieces of armament the anti-gay-marriage side has left.
Like I said before: This is how you know you're winning.