The US Constitution's second amendment was written in a time when owning a rifle was a necessity. It was needed to shoot game for food and to be a part of the Continental army to defend the nation, since in the late 1700's and early 1800's there was no police force or standing military. Times have changed.
Our citizens can no longer protect themselves from all the gun owners who lack the ability to control their anger or those who are or become mentally deranged.
Gun deaths in the USA have gotten out of control and even armed citizens cannot protect themselves when violence breaks out.