The problem with gun registration versus car registration is that there is no real use to having a list of car owners, other than legitimate ones. But, a list of people with weapons would be the first thing any would-be dictator would love to have.

I realize I am inviting the wrath of Godwin's Law here, but, as a real-world historical example of the threat of gun registration, the Nazis:

"In 1931, Weimar authorities discovered plans for a Nazi takeover in which Jews would be denied food and persons refusing to surrender their guns within 24 hours would be executed. They were written by Werner Best, a future Gestapo official. In reaction to such threats, the government authorized the registration of all firearms and the confiscation thereof, if required for “public safety.” The interior minister warned that the records must not fall into the hands of any extremist group."

"In 1933, the ultimate extremist group, led by Adolf Hitler, seized power and used the records to identify, disarm, and attack political opponents and Jews. Constitutional rights were suspended, and mass searches for and seizures of guns and dissident publications ensued. Police revoked gun licenses of Social Democrats and others who were not “politically reliable.”"

http://www.nationalreview.com/article/365103/how-nazis-used-...