Add personal grudges - not “guns”, to mental health issues among the things behind mass shootings. Can you legislate away the combination of personal grudges and mental health issues? No. If the “shooter” could not get a gun, might they use knives, homemade bombs or other weapons? Sure. So legislating the confiscation of guns will do what? Nada.
“... homemade bombs ...”
Largest murder of school children was done by a man with a grudge against the town and likely mentally ill.