What if everyone in the Aurora Colorado theater had been carrying a loaded gun?
Would there have been fewer deaths or more deaths after all the shooting was over?
Two gas bombs go off, you hear guns going off, the person next to you who you do not know pulls out a pistol. If you have a gun do you wait to find out if this person is a good guy or a bad guy or do you pull your own gun and assume the worst?
Now multiply that uncertainty by several hundred and think of ensuing mayhem.