"There are already people out there investigating the feasibility of 3D printing gun parts. It might not be doable now, but it will be one day. Before that happens, simpler weapons like “brass knuckles” made out of super-hard plastic could worry governments where such items are illegal. Weapon laws are not about intellectual property, but they get us to the same place — restricted use of 3D printing. Copyright concerns can and will piggyback on this issue."

Because I couldn't already create "brass knuckles" out of wood in 10 minutes?