It is estimated that 2000 guns per day are flowing illegally across the border into Mexico, a large percentage of those weapons being semi-automatic rifles similar the one used in today's shooting in Aurora. These guns are being used to kills cops, so much so that the cops cover their faces so they or their families will not be hunted down and killed.
There are some guns like a pistol with a low capacity clip that make sense for an individual to have for self defense.
An AK-47 or AR-15 is a gun that is designed for waging war, not self defense. We have a military and a police force to help defend against heinious acts. When we make sure that high capacity assault rifles are readily available to anyone as well as continue to increase the number of weapons of this type in circulation, we are virtually assured there will be more incidents like what happens in Aurora.
Lobbying by the NRA is designed to convince people to vote for increased profits for gun manufactures, and increased violence in their communities. There will always be murder, but there is plenty that can be done to prevent mass murder. Limiting weapons of war is one of them.