As someone who has done DOD work (though not on anything "pointy") I've never felt the need to justify myself in this way. Throughout history, countries have lived and died by the strength of their military.[1] America's global supremacy would not be possible without its military domination, and our standard of living would not be possible if we had to worry about falling under some other power's thumb. Also, while we're at it, we subsidize defense for nearly all the liberal democracies in the world. I feel quite positively about my contributions to all these things.

[1] The study of history is, to a first approximation, the study of war. I am not conceited enough to believe that my generation is the first one that is living outside of history.