On Chopped, it was probably Scott Conant. He owns Scarpetta, a high end Italian place in NYC and franchised a bit, I think. IIRC, he criticized it without even tasting it. I hate snobby rules. People would never have paired pinot noir with salmon if the "white wine with fish" people were treated as gospel.
I think the reasoning is that the cheese is usually Parmigiano Reggiano, which is quite strong, and that it overpowers the delicate nature of fish.
OK, so I don't have a need to grate Parmesan on my halibut, but I'm going to put it on linguine with white clam sauce, or other things with shrimp or crab. Mornay sauce is meant for seafood. And if the food has a lot of garlic in it, the "delicate nature of the fish" argument goes out the door. Balance is everything, and you do need to taste what's in it. But if you like it, ignore what the snobs tell you. Keep an open mind and don't be afraid to experiment.
This is a bit OT for BBQ, but it's one of those foodie things that comes up.