You can have two very drastic views on this issue.
The first would be that you deplore weapons and you do not wish to take any part in taking away another life.
Or secondly, you can conclude that these weapons will be made regardless if you do it or some else does it, so you could at least try to make the more accurate so less civilians deaths occur and/or less of your countries troops die.
I don't know anyone in defense that builds weapons for the love of making weapons. Although, there may be ones. I think for the most part, the people that do it, feel there is a need to build these things, and it's their job to make work as efficiently as possible, but also as safe.
If you don't have this desire, then don't resort to defense. You CAN find other jobs.
Side note, Shackle, it ISN'T ridiculous to be against weapons. I think all of us, to some degree or another wish there wasn't a need and if given the choice between having them or living in peace, I would hope all of us would pick the latter. It may be a something a nation needs, but the ethics question comes in, when is to much? Take a look at the cold war, when did too many nukes happen? Once you make enough bombs to destroy the world, You obviously went to far.