The most dangerous places in America are "gun-free zones," including schools.   Crazed killers have plenty of time to finish their carnage before anyone will show up who can actually stop them. 

The Connecticut school principal had just finished instituting a new school safety policy, which consisted of locking the school doors at 9:30am and insisting that any visitor after that must be identified.  

Or else what?  This will somehow prevent unauthorized entry?  Just after the shootings, a police report mentioned broken glass at the front of the building.   Apparently it was not anticipated that a crazed killer would actually break into the building!  After all, this would be breaking the law!

The school principal was herself killed in the massacre.  If she (or her designee) had been carrying a gun and known how to use it, she might well be alive today and she might have saved many schoolchildren under her care.  

The police are said to have arrived promptly, but by then it was all over.   Their function was to fill out the paperwork.
        
Armed defense at the ready is the only thing that can stop a deliberate massacre.  This conclusion is not rocket science.  More gun control won't accomplish anything except to endanger all of us even further.