The gun free zones that would prevent a mas shooting if a man took a gun into a gun free zone?
Making a place gun free does not mean someone won't bring a gun or two or three or four. On the flipside, these type of mass killings can happen anywhere, gun free zone or not. The basic truth is that very few people do or even want to carry around a firearm, so when one of these lunatics starts shooting at people, nobody can stop them.
As much as I would love to see guns eliminated and for nobody to have guns except for the police, there is a problem with that also. While we currently live with a stable government where we know the rule of law will be followed, there is no guarantee that this could not change at some point. When the people of a country feel the need for a revolution, they need to be armed or they will be slaughtered. Look at what is happening in Syria. Again, we are not Syria, but that could change because there just are no guarantees.
I will take this one step further. It is estimated that within 50 to 100 years, most of Europe will become majority Muslim. Most of Europe has pretty strict gun control laws. What happens if civil war breaks out in parts or all of Europe as it did in Lebanon when the Muslims became the majority and started killing Christians? If guns are brought in form outside of these countries by different Muslim factions, what will happen to those countries? Because we see ours as a stable government, and overall we are law abiding citizens, we think things will always be that way. Unfortunately, as a country, we have only been around for a little over 200 years. Again, there is no guarantee that things could not change at some point.