There are no simple answers... There are no simple or cheap patches that we can use to "fix" this.
Nobody is "normal", the tests may find some who are suseptable to stress but will discriminate against those who may never snap and will not prevent the "normal" guy from snapping.
Bringing guns to the workplace just begs for some very nasty situations to arise, this could turn the normal boss tirade into a massacre.
Added security will never work if someone is really intent on doing harm, look at the bombings terrorists do, no ammount of security stops that.
Zero tollerance policies against violence or threats are a start but will not solve this issue either and may make it worse when those under stress have no outlet when near the edge.
So, what does this come down to?
Well, like I said, we have to look for the root cause, what series of events made people snap? What could have been done to spot the signs or what could have been done to avoid the stress? Could we all learn something about how we treat others and how that has a lasting affect on society in unforseen ways?
So many questions, so few answers really. Why? Because we as a people never take time to look down deep and really examine the real issues that are involved. We just look for the quick way out, the cheap answers, and accept that they will not be effective while saying, "it doesn't affect me"...
I know I've been harping in here, I don't appologize. Someone has to be a social concience and say "hey, something is wrong here!". Well something is wrong here, and I will keep harping to make it right. I will do what I can as an individual and a responsible member of society to make it right.
Maybe all we need to do is treat each otherwith respect, understanding, and compassion. Perhaps when you try that you'll find that it is in your best interest to do so as well.