alt Hacker NewsThis is "broken window fallacy"[1] territory. In economic terms defense spending is mostly waste because a lot of it doesn't get used (hopefully) or gets used to blow other stuff up causing net damage. The fact that it creates jobs is better than nothing, but spending the same money on infrastructure would increase the future productivity of the country.
[1] https://en.m.wikipedia.org/wiki/Parable_of_the_broken_window
The defense budget is a social support program that conservatives will agree to. Rather than just providing people a basic income and healthcare directly, they add the hoop of holding down a job to access it.
It also is meant to keep American industry active (to some degree) in case it is needed.