The comparison you offer up is ludicrous.....crazed fans rioting in the stands and on the soccer pitch vs a parent yelling at a ref.
My self as a coach this would have never got to this point. I would have clearly explained to the parent(s) that their presence would not be required at a game if they persisted with acting like an idiot.
This is a over reaction by the League period! There is nothing in their rules or constitution that allows them to act in this manner.
The whole team signed the document as pressure was put on the few who did not want to sign a document that would cause their daughter to be kicked out of the league as a result of behaviour that they can not control.
A ref if he feels that the fans are getting out of control he/she simply needs to skate over to the home and visitors bench and ask them to handle the situation. If it persists he stops the game until the offenders are removed. He notes on the game sheet the event and sends this to the league.
The league sends out a letter to the Organization of the offending team and instructs them to deal with this issue now.
The organization has a meeting with the parents outlining their expectations and the consequences of their behaviour. Any further display of unacceptable behaviour and you will be band from attending games. They know who the parent(s) are so enforcing this is easy. If the parent is band and they still stay and watch the game then call the police to have them removed if necessary. It is at this point that this parents daughter's hockey season would be in question. Not the whole team.
No need to threaten the team or all the parents because of the actions of one or two parents.
What happened now is bullying.....and the whole team will suffer the consequence if they receive any complaint or they observe any actions.
Play hard, play fair