On the reverse, it only takes one person with a gun to stop a person/people from being killed. People like this loon seek out a target rich environment where he won't be challenged. If just one person near him was carrying a gun, and was trained to use it, he would have never had a chance to shoot so many people.
When the gun ban ended in Washington, DC many anti-gun people predicted an increase in the crime rate. It always does the opposite in these situations. DC's crime rate lowered much more than the national crime rate after the gun ban was lifted.
The Zimmerman situation is one of self defense. It isn't vigilante justice. Also, Martin was not a child. He had a record and was kicked off the school bus for violence and kicked out of school more than once for drug possession. The reason we don't hear about Martin's past is that it doesn't fit the narrative the press wants to push on the public.
Life has inherent risks. I know that if I were in that theater I would have been praying that someone had a gun to pull out and shoot this lunatic dead. I would rather take my chances getting hit with a stay bullet from an upstanding citizen than let a loon with an AR-15 and two handguns wade through the crowd shooting people at random.
Carrying a gun isn't for everyone but I think any citizen that doesn't have a criminal record should be allowed to do so. If just 1-2% of the people in that theater had been carrying then far fewer people would have been shot. Of this I am sure.
Many people think that stuff like this can be prevented but, IMO, the cost to our personal freedom would be too great to even make a dent in it. The only way to remotely stop a situation like this one from occurring would be to ban personal ownership of firearms and this would require wiping out a major component of the Constitution. Then there are numerous ways a person can commit mass murder that would be even more effective than walking into a crowded theater armed to the teeth. The best solution is to have enough people in the general population carrying a gun so that one or two will be in locations where this type of situation develops.
One thing I know that I don't need is government trying to stick its nose in my business anymore than it does already.