The myth apparently began when it was cited by the head of the NRA, Wayne LaPierre, in his 1994 book, Guns, Crime, and Freedom. There he wrote, "In Germany, Jewish extermination began with the Nazi Weapon Law of 1938, signed by Adolph Hitler. In fact, this law actually did exactly the opposite of what LaPierre claims it does. To understand this, we need to step back a few years in history. At the end of WWI, the Germans were defeated, and as part of their punishment, numerous laws were imposed by the Treatise of Versailles on the German people of the Weimar Republic (the name given to the German state during the interwar period). One such law, passed in 1919, outlawed private ownership of firearms, and the government undertook to confiscate all guns currently in circulation.
The 1938 law, then, did not restrict firearms (they were already illegal), but instead did just the opposite, relaxing restrictions on the ownership of guns. As Bernard E. Harcourt documents (PDF) in the Fordham Law Review:
The Nazi gun laws of 1938 reflect a liberalization of the gun control measures that had been enacted by the Weimar Republic with respect to the acquisition, transfer, and carrying of firearms.Thus, the claim made by LaPierre and others is false, and a good example of Bullshit. In particular, LaPierre is only concerned about keeping guns as legal and accessible as possible, and he is willing to make up or repeat stuff without confirmation so long as it supports his position. This is the definition of bullshit, and it raises an interesting political question: How does one engage in a political debate when one side of that debate just makes up facts to support its position? This is a problem that is not just limited to gun control debates, but also issues like anthropogenic climate change, or the economy. I have no solutions to this dilemma, but I think it is the greatest challenge to progress and advancement currently facing the US.