For printing a gun, of course. I am saddened by the interviewed creator's lack of hardcore-ness though:

Personally, I hope that no 3D printed firearm is ever used in a crime, or truly anywhere but a safe environment at a range with proper and full precautions taken.

Or, say to defend someone's life from aggression maybe? It's like hearing gun advocates say 'well if I could live in a world without guns at all...' Oh, the one where women and cripples were powerless against strongmen? Have fun with that.