The Infertility Argument for Same-Sex Marriage

The issue is not whether same-sex marriage is moral, but whether it ought to be legally recognized as marriage.  That quibble aside, Saletan's piece suggests the following argument:

1. Homosexual couples are infertile just like infertile heterosexual couples are infertile: there is no difference in point of infertility.
2. Infertile heterosexual couples are allowed by law to marry.
3. Like cases ought to be treated in a like manner.
Therefore
4. Homosexual couples ought to be allowed  by law to marry.

One can see why people would be tempted to accept this argument, but it is  unsound: the first premise is false. 

To show this I will first concede something that perhaps ought not be conceded, namely, that the predicate 'infertile' can be correctly applied to same-sex couples.  Justification for this concession would be the proposition that anything not F, even if it cannot be F, is non-F.  Thus anything not fertile, even if not possibly fertile,  is infertile.  So same-sex couples are infertile in the same way that numbers and ball bearings and thoughts are infertile. 

But even given this concession, there is an important difference between same-sex and opposite-sex couples.  The former are essentially infertile while the opposite-sex infertile couples are only accidentally infertile.  What the latter means is that there is nothing in the nature of opposite-sex unions to rule out the possibility of procreation.  But in the case of same-sex unions, the very nature of the union rules out the possibility of procreation.  So (1) in the argument above is false.  Homosexual couples are not infertile in the same way that infertile heterosexual couples are.  The former are infertile by their very nature, while the latter are not.  This difference is what justifies a difference in treatment.

We must of course treat like cases in a like manner.  What I have just shown, however, is that the two cases are not alike.

The point is even more clear if we take the view that 'fertile' and 'infertile' are predicates that can be meaningfully applied only to that whose nature includes the power to procreate.  Accordingly, same-sex couples are no more infertile than hammers and nails are dead.  

Read more at Maverick Philosophy Blog.