What' s the point here? To scare everyone from bringing pins to shows so there's no more shows?
I have been attending shows for years. I have never had a problem from bringing pins, nor have I seen a pin get royally abused. What is being described here is the exception, not the norm.
A better topic would be How Show Jerks should be dealt with. I'd at minimum get in their face and depending on the offense possibly see about getting them banned.
You can't just stand there like a disgusted wuss. 500-to-1 the owner wont be there to supervise their pin so it's up to you. We are a community. Treat a show pin like your own. Treat a witnessed offense like someone just pulled that crap in your game room. If you aren't up for the task then proceed to the nearest show organizer immediately to rat them out.
Doing nothing is like letting someone bully you. It will persist if not dealt with.