I had said that the argument didn't address the issue at hand, to which we'd argued briefly about logical fallacies (slippery slope). To the point, he's a good speaker and is skilled beyond my means to communicate without getting ruffled, so I let that slide and went back to work. He's not a bigot, he just knows more about how to argue and understands fallacies better than I.
At the same time, it's a defensive posture I assume when anyone brings up the "soon there'll be nothing stopping a mother and daughter getting married, and people marrying their pets", and that's not fun; specifically for the sudden jolt of emotional exhaustion of having heard that so many times, and then being coddled by the more moderate who say "just wait a while longer, these things don't change overnight".
In many ways, all the arguments have been made - at this point, those who are interested have heard what they're going to hear and are feeling what they're going to feel. Only changes in their lives are going to open up the possibility of a change of mind/heart. He's arguing for the validity of the above positions - in the way that they're technically true, while I'm approaching it of the point-in-time perspective (i.e. *this* change is coming, why are we distracting that point by throwing in other variables).
Anyway, I'd enjoyed his company before and hope to in the future - we just won't talk about these things again.