You're seriously telling me that laws don't exist to encourage good behavior by discouraging bad behavior?
Federal, state, or local?
1) You are completely wrong. Are you really trying to say no bad guy ever used a "gun show" purchase to kill anyone?!
2) Without seeing all the facts, I can't answer that accurately, nor can you. Under my system, Laughtner would have been forbidden already, because he was nutso... it wasn't reported. Etc. That's generally been the case. It didn't happen under the current system because the current system is so weak.
As for your 4 points...
1) Demonstrate how it is? Are you a knee-jerk "shall not be infringed" guy? I suggest you look up the definition of infringe. Infringe is not the same as regulate.
2) You'd be laughed out of the room in most serious circles stating there isn't any problem with criminals buying guns from legal sources.
3) 120k preventions in 2 years... it arises from that documented proof, actually. Your outlying events not withstanding. No system is perfect, if someone suddenly snaps there is really no way to prevent it. However, preventing known wackjobs from getting guns is something we ought to pursue dilligently... since it doesn't stop law abiding people from getting a gun.
4) And needs to be strengthened so as not to be violated so easily... I'm all for pursuing people who falsify on 4473s.