In this thread, I would like to focus on one argument in the SSM debate, which I’ll call the “sterility objection” (SO). I’m going to state the objection as clearly as I can, with the hope that someone will tell me where exactly it goes wrong.
The SO is a response to the argument that SSM shouldn’t be legal because same-sex couples can’t procreate; it argues that if we accept this argument, then we could run a parallel argument against many opposite-sex marriages, which would be absurd. Here’s my construction of the objection:
(1) If same-sex couples shouldn’t be allowed to marry because they can’t procreate, and there are no relevant differences between same-sex couples and permanently sterile opposite-sex couples, then permanently sterile opposite-sex couples shouldn’t be allowed to marry for the exact same reason: because they can’t procreate.
(2) There are no relevant differences between same-sex couples and permanently sterile opposite-sex couples.
(3) Therefore, if same-sex couples shouldn’t be allowed to marry because they can’t procreate, then permanently sterile opposite-sex couples shouldn’t be allowed to marry for the exact same reason: because they can’t procreate. (from 2, 1)
The only way to deny conclusion (3) is to deny one of the premises, because as a matter of logic, the above argument is valid. No one could rationally, in my view, deny (1) because it is simply a statement of the consistency principle: that we should apply reasons consistently, not arbitrarily.
Thus the main problem with SO–if there is a problem–is with premise (2). Opponents who deny the conclusion must deny (2), and affirm the following: that there are relevant differences between same-sex couples and permanently sterile opposite-sex couples. What are those relevant differences?