Mass school shootings are a relatively new thing, where gun ownership has been a cultural constant since the founding of the country. People with mental illness have also been a constant. If the problem is that the meds didn't make enough difference to help, we should see more of these type of events over the past 100 years or more. We don't though.
The changes to the DSM III in the 80's (and subsequent revisions) introduced a litany of "disorders", and the drug companies were quick to respond.
The side effects of SSRI's, which include: mood or behavior changes, confusion, anxiety, panic attacks, hallucinations, extreme fear, impulsive behavior, agitation, aggressiveness, hostility, thoughts about suicide, etc... don't manifest themselves in everyone, which is why 100% of people on medications don't go around committing atrocities. There appears to be correlation that it does cause some people to. Why wouldn't we look there, instead of dismissing it since it doesn't affect 100%? Psychotropic drugs are certainly due a look, to see what (if any) involvement they play in these types of events.
I believe we over diagnose all sorts of made up "disorders", and write a prescription. Just looking at ADHD, we diagnose around 9% of American children (mainly boys) with it, where France has around .5%. They also don't treat it (or other problems in kids) with drugs. Strangely, they also don't have a rash of mass school shootings. Link: Why French kids don't have ADHD
You ever think that maybe there is a profound and fundamental change in our country, our people, the way our children are raised, our society and the general makeup of the American psyche that might be a contributing factor, as well? Blame the meds all you like, blame "made up" diagnoses you don't understand, whatever you like. I still say it's the chicken and the egg - and from someone on the front lines of the fight against mental illness, I think you've got it all wrong, personally.