I agree that "not needed" is, in general, a poor criterion on which to base prohibition. However, even forgetting criminal behaviour, in all of this Americans need to consider the balance between enjoyment of the thing (gun onwership), and the danger of the thing.

Surely nobody "needs" a backyard swimming pool with a built-in life-size blender mechanism, and maybe someone would actually enjoy having one. But we do need to consider the danger that this attractive nusiance might pose to the neighborhood kiddies.

When life-size blenders are outlawed, only outlaws will have life-size blenders.