Let's assume it's all tied to drug abuse. How would you fix that? Drug testing as part of a background check?
We know that won't "fix" it. Drug tests are easily compromised. Besides I don't believe it is all tied to drug abuse. As I said before terrorism is a separate issue, especially in the US where the nutters self deploy after reading some idiotic lies on the internet. Terrorism, particularly Islamic terrorism where drugs are generally prohibited often, although not always, the actor steers clear. But Islamic terrorism is pretty rare in the US. In the last two terror attacks where the socialist greenie white supremacist guy attacked El Paso and the Antifa guy attacked Dayton neither had such restrictions so of course they were both drug users. If this is a rising trend then we have a rocky road ahead.
Some small amount of it is domestic violence related that spiraled out of control but often the domestic abuser is a heavy drug user as well. The Sutherland Springs, Texas church shooter is a typical example of that.
I agree. Many people with mental illness self-medicate with illegal drugs or abuse legal prescriptions.
That is a huge, well documented problem.
And as an increasing number of states de-criminalize marijuana it is possible for many gun owners to fail federal gun legislation without breaking other laws. If the increased potency of pot led to mass shootings then WA, CO, and other states would look like Syria now.
Except a lot of the drugs produced in those states are shipped illegally to other states. The exact amount is unknown because the activity is illegal; but I am willing to bet it is North of the majority of the production. The USPS is a big enabler. The weed shows up in all 50 states.
Due to increase availability and increased potency Marijuana use has exploded nationwide in the last few years in the US. So have mass shooting events. Again you might say "coincidence"; I say correlation.
How to fix it?
The short answer is I don't know.
The long answer is some strategies may help. If a link between the drugs and shootings can be demonstrated in court than this would open up lawsuits for product liability that would end production or greatly restrict usage of many of these drugs domestically and we could go back to 1980 when such events were a very rare occurrence (not accounting for illegal imports). Drug companies have some of the best lawyers in the world and pot dispensaries some of the best propagandists and hackers who use their talents to suppress such information so I am thinking the odds are not good.
We would have to rebuild a huge mental health system to warehouse the mentally ill. Currently prisons and jails are filling that role which is why our prisons and jails are overflowing, they are full of mentally ill people who might not otherwise be there if we had a facility to house them. When we got rid of the mental health facilities in the US the problem didn't go away it merely moved. However, being a danger to themselves and others won't keep people in jail. When their time is up, they get released until the next time. Eventually they do something illegal enough that they die in the process or get locked up for life anyway.
The idea of treating mentally ill people with psychiatric drugs and keeping them within the community has turned out to be an abysmal failure for millions. For some it works but for many others it does not. When it fails we don't have anywhere to put people but jails and prisons.
I just realized I completely hijacked this thread from it's original intent. Apologies to the OP. I believe however this is a discussion that needs to had and trying to have it with non-gun owners is a form of insanity. Traditional gun owners tend to be a bit more practical, logical and open to new ideas that run counter to MSM narrative.