"It isn't for Mars" is just a reasonable inference about how hard it will be for Starship to go farther than Earth orbit. It's over-weight, which reduces payload, which makes in-orbit refueling need way too many refueling flights, which takes too much time and requires building too many refueling rockets that each have 39 Raptor engines @ $2M each if you believe Elon's numbers. It all very readily succumbs to the rocket equation unless the very most optimistic numbers of $5M per launch and 8 launches carrying 150 tons of fuel each are actually met. If not, the only real use of a rocket that big is DoD payloads to Earth orbit.

Didn't Elon have a Twitter meltdown today about how AI will leak your secrets?

The cited Science journal paper answers your question about whether the U.S. govt wants it. As well as the quotes from Heritage and Trump. Sounds like including interceptors (Brilliant Pebbles) is a bit political, but missile tracking is bipartisan (Brilliant Eyes).

I thought it was for chemtrails?

Yeah but OP is backed by citations w/ Nature & Science.