Sweep it under the carpet.
Yep, this is a great idea. If the crime is not filmed, it did not happen. Problem solved.
So in the future in a case like the school kid fight, the two involved in the fight get suspended. The person filming it gets arrested. That sounds fair.
I agree that trying to discourage copy catting is a worth while aim, but the ban hammer? Is that really the best you can come up with?
To me the only time you should be able to go down that road, is if you can prove that the person who caused the assault also caused the filming. I.e like the assault versions of a snuff vids (which I am not sure ever existed). In which case you just go after the assaulter even more than you normally would.
But an completely innocent 3rd party filming a crime should not be punished as they are essentially making a record of something that has happened, like journalists do.