xxyy beat me to it - I was going to suggest he has a wee think about where all the funding is coming from for all the 'queer' groups that have taken over pride, etc.
Overall, though, I might try and take a step back from the 'debate' and look at the motivations behind it. I wonder if this is all a manifestation of anger from him? Where is it coming from, is he strongly motivated to do 'the right thing'? Is he looking for a cause, and if so, why this one?
I would look for common ground, and ways to keep communication channels open. I would probably avoid the hot button topic for the moment, and try to work on active listening.
*When he hits upon something he can't explain, that's when the names, the flouncing and the "just be nice" start.
It's pointless trying to explain anything or open up a debate.
He's firmly entrenched.*
This demonstrates that this is an emotional issue, not a logical one. The cognitive dissonance is there, but he's defending himself against what, on some level, he knows to be true. I'd just give him space to try and encourage him to relax a bit, maybe. Too easy to get into an arms race or power struggle.