I find it helps to think of the military as a socialist style make-work jobs program. That's not it's only function, but it is an important one. For the poor (boots on the ground types) it educates them, feeds/houses them, teaches them self discipline. During peace time it's an important economic ladder. For the middle class, it's about creating work for engineers, programmers, and scientist types.
During peace-time, I think there's a lot to be said about the ROI for the military, if the military is at some reasonable scale (which I think it is not).
With regards to the many Middle East (ME) wars, I think a lot of that is about maintaining and enforcing the petro-dollar. If the ME decides to start selling their oil in Euros or gold or some other currency, it will mean the end of the USA as we know it. The dollar will collapse and China or Russia will take over as the world hegemon. Many people really have a distaste for US hegemony, but unfortunately the real options on the table are not US vs nobody. It's US vs probably China. So the ROI is much more complicated in that regard.
The military has and will continue to be the politically-correct [to them] means of implementing a welfare state for republicans. I mean you get free high-quality insurance via tricare, free college via the post911 GI bill, subsided home loans via the VA — all the trappings of the welfare state but politically acceptable to most Republicans and centrist Democrats. The military-industrial-congressional complex is alive and well.
IMO there is no reason we should be killing people outside our borders or even have military outside our borders when there are much larger domestic problems that are unaddressed. I walk by homeless people shooting up right next to million+ dollar houses (yay Seattle + AMZN/MSFT) every day and fixing this shoes not seem to be the priority as the defense contractors and American people themselves are from this porkbarrel.
Of course war is a racket. And I agree with you that the US has been fighting wars of aggression and generally behaving in a despicable manner. Now, let's imagine what happens if/when the US decides to stop being so aggressive. I believe the Middle East begins to trade oil in Euros, gold, Yuan, or some other currency. Demand for the dollar collapses. The US economy collapses in a spectacularly violent way. Like a Venezuela/Zimbabwe kind of spectacular economic collapse. Then China, who is already putting Muslims (Uyghur) men in concentration camps and assigning rapists to live with their families and educate them into being good Communists. China who is committing mass murder to fill the market for human organs. China who is already colonizing Africa. China which is an etho-state with a dictator for life. China is going to start really flexing more around the globe.
What is your hypothesis on what happens across the globe in the absence of US hegemony and crazy wars. Do you believe a loss of the petro-dollar would lead to US collapse? Do you believe Chinese hegemony would happen, and if so, would it be better or worse than US hegemony?