The law of unintended consequences springs to mind...
In reality, when something "kicks off" unexpectedly, it's often confusing, frightening and doesn't play out the way anyone expects.
If you have people tooled up with guns, tasers, sprays or whatever - things are going to go wrong, because untrained people with no conflict resolution skills, with no ability to control fear or know how to deescalate - are going to make bad decisions.
This idea, that because you're walking around with a weapon somehow makes you safer, when applied to large groups of people - is drastically wrong, and totally counter productive.