Hockey is not as violent in spectator sports as soccer is in which violence practically occurs at all games, from specators and players alike.  I don't know why the referees in soccer don't strike.  This is why should, all parents and coaches must pass a rules test before they are allowed in the rink.  All parents are biased to their child and to the child's team.  If a player on the other team gives their child a lovetap, a major should be called but if their child skates hard from one end to another and hits a player from behind and wonder why their child had gotten a match for attempt to injury, when he shouldn't even gotten a minor penalty for it.  

Parents should know that referees are not biased to any team even if they have relatives or friends on a team.  The referee would call the same penalty if it happens to the other team if the referee is on the otherside of the ice if the referee is working a two man system.  The referee if they are doing a three man system would call it the same as while.  Note that every play is different.

First, I would like to say that I am a hockey referee. 

Second, this only shows that parents are pushing their kids to become NHLers or goons.   About 99% of the players that are on the ice will ever make Junior or College much less the NHL.  They should let the kids play, the coaches coach and the referees ref and as a spectators watch the game.

I have heard parents yell "Hit him!" in a game that has no bodychecking and when there is a penalty for it, they scream like it was a little lovetap.   If referees called every penalty as described in the rule book, no one and I mean no one would be on the ice.  Every player breaks the rules even Wayne Gretzky but no penalties are called because a)  the player never made contact with the other player, b) it was an accident, they were going for the puck, c) the penalty was a insufficient penalty behind the play, ie  a trip or light hook) 

Third, yes, referee's make mistakes like everybody else but that gives no reason for a spectator even if the spectator's child to go on to the playing surface or hit another person.  I have never refereed a game in which there was an injury in which a player was taken off the ice for the rest of the game.  It's ok to scream once when the incident occured but after that they should watch the game.  They should be more involved in cheering their chld on than to berate a referee or linesman who makes a mistake during or after the game especially if the play didn't involve an injury or a dangerous play.  The referees and linesmen call what they see.   Also, if they are doing their positioning correctly, they are in a better position than any spectator or coach.  I remember once I was on the goal line and a player shot the puck but the goalie stopped it but the goalie's trapper went all the way into the net and I called a goal.  The puck wasn't in the goalies trapper for more than a second before the the puck had crossed the goal line therefore it's a goal, no matter if it's in the goalies trapper or pads.  I could hear everyone screaming but I know I was right because I was in the correct position and I saw the trapper where the puck was in the net 100 percent.