Are you kidding? Does the name Timothy McVeigh ring a bell?
They changed security requirements on federal facilities after that. I worked on a few projects for the VA where you couldn't get a vehicle within 50' of the building. Granted, someone could walk in with a bomb strapped to him or a machine gun, but at least the whole building wouldn't be taken out.
As for the gun issue, you could make them as illegal as could be a someone determined enough could still get one on the black market. Drugs are illegal and people get them all the time.
As for the culture of violence, I agree with this mostly. Violence is glorified in TV and movies. If there aren't enough explosions and bodies, we complain it was dull and lacked action. Video games are even worse. There's another shoot 'em up. game every 5 minutes. You're actively fantasizing about mowing down space aliens or the Taliban.
As for the guns, I would say leave the semi-automatic weapons to law enforcement and the military. You want a gun for hunting or self protection or just to fire off a few rounds at the range, great. But what do you need an uzi for? Worried about the zombie apocolypse?