Without weapons you cannot have an army, and without an army you are instantly conquered by some raging lunatic despot who happens to have one. Having more advanced weapons than the loonies is a blessing IMO.
Saying "I don't feel comfortable doing X" is not the same as saying "no one should do X". I'd feel the same about not wanting to work for a casino, or a lab that makes better tobacco products, but oddly enough not a brewery.
OK now justify selling weapons to the loonies like 90% of arms manufactures or their customers do. For last 50 years, US enemies fight using US provided weapons.
And what happens when the conquering despot is my country (Dick Cheney's team)
That's foreign policy, that doesn't have much to do with the manufacturing of weapons. Weapons manufacturers just provide weapons to their country and it's the country's (politicians) job to make wise use of it.