Many promising young researchers from around the world earn their stripes at US universities, and loads of them would be happy to stay and become Americans. Unfortunately, the US immigration system makes that difficult and lots of them get sent home.
The best part about that plan is they don't even have to develop their own AI weapons. They could deny that capability to adversaries just by allowing those workers to take up interesting & lucrative jobs in the American civilian economy.
https://www.bloomberg.com/view/articles/2018-05-31/u-s-shoul...
They're a very long way from there, see for example this: http://defence-blog.com/army/combat-tests-syria-brought-ligh... (which also happens to be my latest separate post submission). People tend to over-estimate the technical prowess of the Russians, there's only so much that the military of a country with ~160 million people can do to technically compete against both the US and the EU.
I think the citizens in Afghanistan, Iraq, Libya, Syria etc. are quite happy that their liberty is protected. :-(
However this is completely irrelevant to the point. The question was why do we need to have a superior military to our adversaries, and the answer is because our adversaries are real, and if we care about our liberty we need to take them seriously. To say otherwise is either laughably naive, or is an outright rejection of liberty. Try refusing to work on military contracts in Russia or China and see what that gets you. In China, your career pretty much has a hard ceiling unless you want to join the communist party.
Who were strongly financially supported (and thus in some sense "enthroned") by the CIA:
> https://en.wikipedia.org/w/index.php?title=Taliban&oldid=846...
"A while later, the U.S. CIA and Saudi Arabic General Intelligence Directorate (GID) funneled funding and equipment through the PakistanI Inter-Service Intelligence Agency (ISI) to the Afghan mujahideen."
The value of (relative) freedom made the US powerful. If the US becomes just like the bad parts of China or Russia, who cares of China or Russia come out on top instead of the US? They will have already won the war of ideas.