It is probably less than 50% of parents that have played at best, and I'm not counting the dad that started playing beer league at 28 years old and thinks because they started watching hockey in 1990 knows everything there is to know about the game and how it's supposed to be played, just parents that grew up playing the game and have that as a point of reference.
I agree that Mom's yell the loudest and that Dad's are on the refs the most, but again I feel like these are the parents who didn't grow up around the game and think they know about the game, but actually "know just enough to be dangerous". These are the parents that I never wanted to be anywhere near when watching a youth game. There's a reason that, from my experience, that the parents that grew up around the game for the majority of their lives are usually the parents who watch the game from a corner of the rink away from the shit show that happens in the stands.