Can't deny many are irresponsible
Generally the folks buying modern military style weapons didn't appear to be buying them for deer hunting but in preparation for the "end times". They want to be ready to fight off the invading terrorists, drug-addicted mobs, the IRS, or the Four Horsemen. These folks seemed to be a little unhinged and looking for an opportunity to use their weapons, but I don't believe these people would be the type to shoot up a school or theater. However, I do believe they can be easily pushed over the edge and use their weapons on their spouse and children then head for the hills and wait in a cave for the rapture. Statistically, the ones in the most danger from these types of gun owners are the spouses.
As for the "responsible" gun owner I'm sure there are some. I am also sure there are a great number not so responsible. These folks keep their guns in a closet, in the car trunk or glove box, under the bed, in the night stand or as I did in my youth, hang them on the wall. In order to be of any protection guns have to be readily available to stop the terrorist (or the meter reader) coming up the driveway. If the NRA is serious about supporting responsible gun owners they need to figure out a way to keep guns away from the irresponsible folks.