Good intentions can backfire
"Reasonable gun laws" allowed Hitler, Stalin, Mao and others to round up the guns, then easily round up and slaughter 50 million-plus innocent people. Since feudal times, when the lords kept the serfs unarmed, those who wish to rob, subjugate, enslave or persecute others have contrived to disarm their intended victims on some pretext or other.
Well-meaning politicians, reacting to demands that they "do something about gun violence" declared schools "gun free zones," making them irresistible to mass-murderers, who love a defenseless victim pool. Why do you suppose they never attack gun stores or shooting ranges, as one would expect if availability of and proximity to guns were really the cause?
What if every gun in America had been confiscated, as the Left fantasizes? Lanza could, as easily, have killed his mother with a kitchen knife and run down 20 children with a Prius while they waited for the school bus.
He did not need a particular type of gun, or any gun at all, and banning them or further vilifying and harassing law-abiding gun-owners will not prevent future murders. It will just leave Americans defenseless -- forever.