I've had GD "twice" (according to my OB at the time) and in my experience most obstetricians absolutely freak out about it.

My obstetrician with my last pregnancy was still demanding I be induced at 38 weeks because I had insulin dependent GD with my first baby - even though the second pregnancy I passed three GCT's, was self monitoring my BSL's at home (which were fine) and was following the GD diet. I didn't have it, he was convinced that I MUST have it because I was insulin dependent first time so there was just no way I couldn't have it. Idiot.

I agree that if he's freaking out about something that isn't even an issue yet, and getting you wound up about it as well he's probably going to be someone you're going have to battle with in labour...you don't need that, if you can change I would consider it.

I wouldn't waste your time or precious energy at this point trying to convince him with research etc. If he's over reacting like that it doesn't matter what you show him he is not ready to accept that his view on this issue has no scientific basis. Far easier to find someone who you don't need to convert iykwim.