Bombs don't kill people either. Not on their own - they just lie their on their own doing no harm to anyone. The same goes for canisters of poison gas, or ampoules of anthrax. Totally harmless unless some human being comes into the picture...

And 'arms', I would suggest includes all those things. Isn't it great that Americans have the right to stock up on stuff like that, and any laws to stop them doing so would be unconstitutional.