As ecto is saying over and over again, though a gattling gun isn't exactly necessary, it IS legal, and it is part of our rights, as such, it must be protected and respected until it is deemed illigal by a legislative body.
Also if my neighbor had a gattling cannon in his garage, I would so totally visit every day.
Lastly, the idea that weapons bought legally are used to kill someone illegally is, in general, proposterous. True, some people do kill others with their legal firearms, however, gang violence and other sources of deaths, are majorly cause by black market weapons bought illegally, and restricting gun ownership would result in high crime rates, as is evident in great brittain.