Anything could have set him off, he was already planning to do bad things at some point. That's not what we're usually talking about which is your average everyday people. Extremists will use any opportunity at their disposal but they are not the people I want to focus on (though that is me speaking personally not speaking on behalf of anyone else). I'll leave that up to the FBI. Meanwhile I'm more concerned about my friends who have known to be up and down with periods here of depression and my friends that suffer from anxiety, my friends who are on the verge of losing their jobs or already have, those are the people I want to focus on in respects to how we can realistically help out.
I get where your viewpoint is coming from though