Defensive weapon or deadly weapon ?

On February 14, 2018 there was a shooting at Stoneman Douglas High school which took the lives of 17 people and mentally damaged the family's that lost members in this tragedy. The shooter; Nikolas Cruz was using an AR15 which they use in the military.  But what if the United States had a law where you could only purchase hand guns such as pistols, would the Stoneman Douglas tragedy have happened?  Would Nikolas Cruz have taken the lives of 17 innocent souls?

There is a lot of controversy on if we should or shouldn't be able to own machine guns. People say that we have the right to "bear arms" and should be able to purchase machine guns. But we as a group don't believe it is so necessary to use such powerful guns as defensive weapons because of the fact that hand guns are just as powerful as machine guns. The world record for how fast a handgun can be shot is 3.7 seconds, with the use of 27 rounds. Crazy right ? So if you can do 27 rounds in 3.7 seconds with a hand- gun, why is it necessary to use machine guns as a "defensive weapon" ?