The Colorado incident is a tragedy for all involved and no tonnage of laws could have prevented it. In every land where private ownership of firearms is prohibited, the criminal element (i.e. anyone who wants to get one) has no problem securing weapons - it is all a matter of cost and it is often less expensive to purchase weapons off the street than in the local gun shop.
HOWEVER... my wife carries a compact .380 with a laser sight and could have taken the shooter out before he got off more than a very few shots thereby saving countless lives.
The vast majority of gun owners stand with law enforcement and are as interested in protecting their neighbors as they are in protecting themselves.
Las Vegas, Nevada