What can you prevent?
Can you figure out who's crazy and who is not? Well, no. It can be hard to tell, especially if someone is crazy and also smart. Or if someone is crazy and has no access to health care.
If you could figure out who is crazy, would you be able to accurately assess who is crazy and violent and who is just crazy? No.
If you could single out the people who were both crazy and violent, would you be able to enact restrictions on their access to weapons that actually kept them from obtaining them? No, that stuff never works.
Could you make guns illegal? Why yes, yes you could.
Yeah, and don't give me that - Australia did it, and if there were ever a country more testosterone-soaked and frontier-oriented than ours, it would be Australia.
The fact is, if this kid hadn't had a gun... you can't kill 30 people with your bare hands and the worms in your brain. Bombs are hard, and require more organizational skills than most mentally ill people possess. Even the Unabomber only managed to kill 3 people. If my little stalker in the 80's had had a gun, he might have shot my sweet protective friends (Rudy, Chip, Dan, etc., I am still humbled), and all our lives would now be ruined.
And this is saying nothing of the everyday violence that permeates the criminal trades. It's hard to believe that there are compelling arguments for free ownership of guns that trump the mortal and economic cost of gun violence in this country.
On the other hand, the fucking Supreme Court today says that "government has a legitimate and substantial interest in preserving and promoting fetal life." Go fetuses! To hell with pregnant women and college girls! Our friend at VA Tech would have gotten in trouble for performing a life-saving medical procedure on a woman which would have killed one fetus, but he could legally buy all the guns he wanted.
Not everyone has good impulse control, and impulse is all it takes to kill a person when you have a gun.
(AH, I think we're going to have to agree to disagree here. I know I'm not going to change your mind, and in fact, I think that if guns are legal in this country, you should have some.)