Richard Chappell critiques the published version of Robert George et. al.’s article that the Lure mentions here. He, but not we, makes explicit the irrelevancy of metaphysics to the law. Both raise counterexamples to the specific conception of marriage on offer (I prefer his vaginism counterexample to our erectile dysfunction one, but that’s just aesthetics). He goes beyond the “organic bodily union” argument to raise solid objections to some of the policy boilerplate.
One oddity that neither post explicitly flags is that there’s very little intellectual connection between the authors’ metaphysical argument against same sex marriage and the hodgepodge of policy considerations [bad for the children, bad for the institution of marriage, etc.] they adduce against it. In fact, if they really do buy that gay marriage is a metaphysical impossibility, it is surprising that they also think it is morally wrong. (On the face of things, forming moral opinions about metaphysical impossibilities doesn’t seem a worthwhile pursuit.)
By way of partial explanation, it’s instructive that they decided to publish in a law journal. The policy arguments, particularly, are couched in judge-quotable language [tenuous causal connections presented as though they are What Sensible People Know]. Though I could also imagine some of the grand-sounding metaphysics appealing to, uh, Justice Kennedy. The point, though, is that it makes sense to write a smorgasbord when the goal is to offer up an armamentarium of rhetoric to judges already inclined to your point of view – less so when you are trying to present what you really believe, and why.
Gratuitous picture of Robert George and Justice Scalia schmoozing Catholic-ly, here.