A gun was drawn on the murderer in the Clackamas shopping mall shooting recently. He did not fire for fear of shooting an innocent bystander. But when the gun was noticed, the murderer shot himself. I hzve read, perhaps here, that that is what happens..when they see the law enforcement, they shoot themselves. So perhaps even unloaded guns would have some effect.

Count on it...innocent people will be shot by people shooting the killer. It will happen. But it might save 10 lives and cost 1. And I don't think all those other scenarios are likely..50 people being shot because everyone is shooting everyone else. It usually would be clear who the murderer was.