Exactly, I scream with my kids. And we don't do it in public, only at home. It's just a way we have fun. I have also been known to shriek at the top of my lungs driving down the road with the music blaring, but once again I'm not affecting anyone else.
I asked why it's a bad thing and apparently my kids can get in trouble at school. That still doesn't explain to me why doing it at home is wrong, especially if everyone is enjoying it. Part of growing up is learning that different situations have different rules. There are times when laughing is inappropriate, but no one is suggesting that kids should never laugh. And I have heard children get REALLY loud when laughing and playing. That behavior is encouraged in the right setting, but screaming for fun is not. I just can't see the difference.