If you make a hammer, it can always be used to murder someone, but if you make an AK-47, there's only one way it can be used. So if you don't want what you make to be used for killing, don't make an AK-47. If you 're good at toolmaking, choose to make tools that are not weapons.
We want to perform our work skillfully, effectively, and professionally. But we never want our tools to actually be needed.
(Another is that we can't effectively create a shield without the risk of it being used as a sword.)