We've had by far the greatest firearms proliferation in the Western world for centuries. In the 1920's you could buy fully automatic Thompson sub-machineguns from a mail-in catalog. ( http://www.nfatoys.com/tsmg/web/coltguns.htm ) Yet school shootings are a relatively recent (~30 years) phenomenon. Over that same 30-year period we've also had an increase in single-parent households as well as an increase in SSRI drug prescriptions. There doesn't seem to be anywhere near the willingness to attack those social issues or investigate their impacts on murderous outbursts.
Firearms proliferation seems to work well for Kennesaw, Georgia. https://edition.cnn.com/2018/03/06/us/kennesaw-georgia-gun-o...
But the data for everywhere else is a mixed bag: https://www.rand.org/research/gun-policy/analysis/concealed-...