Champions are not made 3 nights a week. It takes dedication at home as well. We totally encourage parents to come on to the mat and help and we we don't have a closed practice but we do require everyone who is on the mat helping or giving instruction to have a background check and a coaches card. IMO anything less is a risk and liability to the wrestler and the club.
And if the "wall flowers" get too loud or cause a distraction we have been known to tell that person to step outside or even clear the room.