With over 300 million guns in circulation and millions of those similar to the assault rifle used in this case there is not going to be a way to prevent anyone from obtaining a firearm or prevent incidents like this from taking place.  That doesn't mean that those in love with the idea of self defense using lethal force won't view their rights as under threat but as a practical matter there will be no meaningful regulation of the ownership and possession of guns.  The level of gun violence is just something that we need to live with as it will never go away.  The best we can do as a society is make it clear that the "good guy with a gun" has no moral high standing and is just one more miss away from manslaughter.