That may be true but doesn't matter. The fact that weapons will exist and even the fact that they must exist, and even the fact that you benefit from them exist

That may be true but doesn't matter. The fact that weapons will exist and even the fact that they must exist, and even the fact that you benefit from them existing, none of that means you are obligated to work on or with them yourself. Cakes exist and I even like them, and I do not choose to work at a bakery.