I really don't understand AG's argument. Do you?
Yes.
:^)
More seriously, I understand your frustration, but sometimes it's best to be a bit philosophical about these things. As nearly as I can tell, the blow-by-blow went something like this: he made some point, you challenged him to back it up, he declined, you suggested that his refusal was because he can't do so. And having made that final point, you might as well realize that you can't make someone answer you, so perhaps it's best to just leave it there - if you want to conclude that he can't support his contention, whatever it was, that's fine, but there's not much point in harping on it after that. Everyone's made their positions clear, neither of you are changing your minds, so why not move on? Fewer ulcers that way, trust me, especially because you'll see that again and again ;)