Make gun providers responsible for criminal acts with guns

Make the persons who directly allow criminals and deviants access to guns criminally and civilly responsible for the results of gun violence.
Those who through negligence, profit, or facilitation allow deviants to terrorize and create havoc should bear the criminal and civil brunt of their negligence.
Making them personally responsible for their buyers or close acquaintences would cause them to think deeply about allowing guns in the hands of unstable individuals.
It would bypass the need to argue constitutionality of gun ownership and make dealers and individuals responsible for ignoring deviance for profit or foolishness.