Allow me to get all political on your asses...
I just want to say that before you read all this, it sucks a guy was killed.
The thing that a lot of people don't know about guns on airplanes are these facts:
1: Air Marshalls have been flying with guns for a long time, something like 30 years. Since the start of the program at any rate and I thin the Post said it was in the 60s or 70s.
2: A handgun fired in a plane, even if it directly strikes a window, is not going to cause a massive depressurization of he plane and kill everyone like in the movies.
3: Every system in a plane is at least double redundant. If there is one thing the government does right, it is redundancy. There is no point failure source, except for the pilot and people on board.
DISCLAIMER: The part about the plane's redundancy comes from my brother who works with some guy who flew for the military. As I have not met the guy, it may easily by false. Still, it sounds true enough to me.
And one final note, I don't think we are criminalizing mental illness, so much as ignoring it until it becomes a criminal issue. Which is criminal in another sense. There were lots of state mental institutions until taxes were cut in the 70s and 80s. Since the 50s, our government has been slashing taxes. Our current tax obligation is the lowest ever.
Taxes: they aren't a burden for those who believe in social responsibility.