War is an ever-present possibility - do you want your neighbor's kids (or yours, if they join the service) dying or being maimed because you didn't help with what you know?
1000 years ago, if you were a blacksmith and the Vikings were coming, would you make swords or ornamental railings?
People who think "it's unethical to make weapons" always assume that someone else is making the weapons, which makes them feel good about themselves (not sure why) - they're willing to sacrifice themselves and their neighbor's children for their ethics.
I'm not. I make weapons, and I think the 'ethical' stance on defense is really just virtue-signalling.
/Edited. ;)