You know, have we considered maybe a massive increase in sporting leagues? The kind where generally people don't get murdered?
Training people to kill each other and then having them do so seems a literally sociopathic way of accomplishing the end of physical fitness and giving people a purpose, no? A massive network of athletic tournaments and government-subsidized athletes would probably be a lot cheaper for the outcome too.
I get this isn't really why we have militaries (I think? I hope?). I honestly think it's a pretty ridiculous suggestion to make that it is, or that it justifies them. If the military expenditure is to be justified, it's sure not for that.
Then again there's a lot of consumer tech that comes out of military research like the internet.
Same could be said of any sufficiently large government run programme. Military, healthcare, social security, etc.
Also, military provides plenty of people to
a) have a purpose b) be physically fit
Military spending also provides stable economies for a lot of countries.
Also conflict seems to happen in regions where there are no military spending.
Would US have gone into wars with Vietnam, Korea, Afghanistan or Iraq if they had military spending (or nuclear warheads)? What about Russian invasion of Ukraine, Georgia?
Paradoxically may be its best that every country have strong military spending and a decent proportion of the population who are physically fit and working on technological advances even if it's military related. Innovations out of military almost always benefits general society.