I call it a trap because much like the debate at hand, there is no logical benefit to one side and they can only lose. That is, of course, based on the concept that the argument is win/lose which, in my opinion, is exactly the road they took us down. I'm saying this as I perceive their point of view to be.
If they say the gay couple, they have absolutely no justification and are only saying it to be hard headed. If they say the straight couple, they lose. If they say neither, OABB unleashes on them and we repeat.