Holding soldiers responsible for the wars they fight would require giving them the option to refuse to deploy, or to refuse to fight while deployed. Currently that's punishable quite severely

We could do a better job punishing soldiers for war crimes. But responsibility for the war itself rests with the President, congress, and the ones with power over them (which is supposed to be the entire population, but the top 1% do have an incredibly outsized influence in US politics. Not that I think it's healthy to codify that)