Here's my short theory on the rules of the Kon, after my three years of attendance:
Yes, it sometimes feels at times like you're being told not to have fun anymore. You can't travel through the halls at more than walking speed, you can't tackle your friends that you haven't seen in ages, you can't wear entirely realistic costumes, you can't play with the props you spent all year working on, you have to wear a silly little tag around your weapon that makes it look neutered in photos.
But remember that the NDK staff (some of whom, the volunteers, I've known personally) are not the highest form of government. NDK enforces the laws of the Denver Police, the police enforce the laws of Colorado, Colorado enforces the laws of the US Government. Somewhere up the line, someone was scared as hell of kids being accidentally shot by police officers who thought they were in a life-or-death situation. And that someone passed down the line the edict, "avoid this at all costs." Then it was left to the lower levels of the chain to decide how to avoid it.
I'm going to guarantee, no one but no one in the NDK staff WANTS to ruin your good time. But if they don't follow the chain of command, the whole Kon gets shut down by the powers that be.