Over 60% of murders in the United States take place with a gun. Many people say that it is an American's right to "bear arms". It still is, although many people do know how to use/care for a gun, the majority do not. There is a LARGE difference between owning a gun, and knowing how to use/store it responsibly.
Self-defense is the most common reason for owning a firearm. Fear of home invasion, robbery or just getting "beat-up", are just a few of the reasons that people feel that they must own a firearm. The lack of understanding of how to use/store the firearm has led to countless innocent deaths. It is 43 times more likely to kill a house member than an intruder with houses that contain firearms on the premises. Not only is "self-defense" an excuse to own a gun, many people claim that the framers of the constitution meant it to be this way.
Although foreign invasion was a big problem back when the framers were around, it no longer is today. The United States military is the strongest in the world, and even if the United States were invaded, it will draft up the "average Joe", and teach him how to use a firearm properly.
Although there is no stopping a "black [firearms] market", there are ways to cut down on it. Gang violence is a big problem for most of urban America. The typical gang member is 19 years old. If the buyer of a firearm had to take a "safety" course, how many 19 year-olds will actually sit through one of those? By more or less cutting off the "legal" gun supply, there will be fewer firearms to shoot with overall. Fewer firearms mean fewer shootings.
Simply giving a government run "safety" course in firearms safety/storage to all prospective new gun owners will, over time, lower the total amount of gun deaths in our country; this stance is far less "radical" than the majority of "gun control" proposals.