A point I've been wondering about myself.
Simply adding a few million dollars and some new facilities to existing detection programs on Earth would do wonders for the system as a whole.
I can think of no function that could be accomplished on the Moon that could not be accomplished by, at most, Hubble-type systems in Earth orbit or nearby.
The technology and propulsion systems required to shove an asteroid out of our way is something you would acquire at least as easily from a Mars program as a lunar one.
Now, if you were building nuclear or solar-powered catapults to "nudge" asteroids with terminal-guided Moon rocks, you might have something.