Seems to me the breakdown was in our handling of the mentally ill - the current paradigm is let them go about their business until they start killing people. If we kept guns away Cho, what would have stopped him from driving a vehicle at top speed through a lage crowd of people - his only goal was to kill as many people as possible.
He might have done what nut in Norristown Pa did a few years back.
Bought a black powder revolver through mail order.
Killed and wounded a few folks before it was over.
Perfectly legal!