A person with mental problems is more likely to shoot up a school than a sane person. A person with mental problems is also more likely to be on some kind of antidepressant or antipsychotic. My take on that is that it is the mental problem that is the root cause.

That said, during the first month or so after a newly introduced antidepressant there is an increased risk for suicide or violent behaviour. The medication does not in itself introduce those thoughts and tendencies in the patient, they are there already. They simply make the patient better (not as often as we would like, but still) and more able to act on his thoughts, whatever they are. If a patient has a severe depression, those thoughts are usually a bit on the dark side. So before more normal thought patterns are established, shit can indeed go south. That is why a patient with a new psychiatric medication should have frequent follow-ups, something that isn't done nearly enough.

Here's a thought: perhaps the direction society is moving towards is causing depression. Perhaps women being pushed in the workforce is leading to depression. Perhaps men who are leading homemaker lives is leading to depression. Perhaps forcing integration and equality and acceptance is leading to depression. Maybe we need to let the natural order of things operate without us interfering and pushing for change that we think is "good" for society. If we start tampering with how things naturally developed and create an artificial, forced society, we will all probably end up on the happy pill since nothing is the way that it should be.

Downvotes and criticism are welcome, this is a really touchy subject so I understand