I support 3d printing of weapons making the issue obsolete, since they could be produced when and if required.
The issue is that some people, maybe even most of them, try to be correct and right, and don't wanna print a fire weapon at home if it is illegal to have one.
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I think you mean, that statement is true except when it isn't true.
Any number of cases can be cited. Rampant ethnic cleansing in a country torn apart would be one example.