Guns don't kill people. Mentally unstable people kill people. They do this with guns, bombs, and in many other gruesome manners.
Banning guns will not stop future tragedies such as the killing of innocent children and teachers in Sandy Hook, or the massacre of innocent movie goers in Colorado and countless other horrors from taking place.
We need to educate ourselves on mental health issues, and have safe places and easy methods to have loved ones "committed" to receiving mental health care / medication so they do not hurt themselves or others.