The ISS served all political purposes it could, and microgavity research can be served by private entities these days. (Especially considering that a Starship has half the internal pressurized volume of the entire ISS, at approximately one thousandth the cost.)
A permanent Moon base would allow research opportunities that private LEO stations can't: ISRU, low gravity research, the far side of the Moon offers unique opportunities for astronomy (any spectrum), etc. pp. Long term, who knows what additional opportunities it opens up.
in space travel there's a saying: once you're out of atmosphere you're halfway to anywhere. it takes tons of energy to get over the friction of air resistance. That's way we want a future where space-related things are built in space as much as possible. Once we can solve the idea of permanent installations on the moon it will have several advantages over an orbital station such as ease of additional construction, potential local resources that don't have to be shipped up and the ability to establish a base that can manufacture the things needed locally from imported or local resources rather than needing to manufacture things on earth and then launch them assembled.
I think it's more escaping the gravity well, as the energy consumed by air resistance is fairly negligible compared to gravity and is more of a stability issue. But yeah, once in LEO you're halfway to anywhere as long as you can bring enough mass up for what you need.
Yeah, the atmosphere complicates things a bit during launch but much bigger issue is gravity - Earth having the highest gravity in the Solar System among solid surface bodies.
For landing hovever it makes things signifficantly easier! You can break full arrival speed from lunar or interplanetary space (successfully done by Apollo missions) with a relatively light passive heatshield & land on parachutes. You can even brek to orbit instead or use the atmosphere to change incliunation of your orbit and other tricks (there are proposals for air breathing ion engines, etc.).
Lack of sufficient atmosphere is what makes landing on Mercury (no atmosphere, need to break to zero using rcoket thrust) and Mars (enough atmosphere to break from arrival speed, not enough to use parashutes or gliders for a soft landing) so difficult .
that's fair, I was kinda just inferring as someone whose space travel experience is limited to Kerbal Space Program. The point still stands though: whether it's atmo or gravity the moon has a lot less of it than the earth, but still has a lot more local resources and space to put things semi-permanently. Long distance slower than light space travel has a Sahara problem and at least in the solar system the same sol'n could be used: leapfrogging from cache to cache. The ISS is a better cache than the nothing that was there before it, but a functioning moon base would be an amazing cache from which to launch ops into the deep solar system.
If there is water ice there, as suspected, it is the most realistic path to a self sustaining space economy. If you can earn money in space, there is a reason for people to work in space, and you can extend the economy into space.
"Close" means a different thing in Space than it does on Earth.
If the planets are aligned the Delta-V is not that different between the two (Mars is about twice as much Delta-V for 100x the distance). You can use aerobraking in the Mars atmosphere but can do no such thing on the Moon. And then the last problem is that on the Moon you need to budget for a round trip, but on Mars we could produce fuel on the surface for the return trip. When you start thinking about all that it's obvious that Mars makes more sense.
Can we actually? And I mean in any reasonable time frame say 100 years? And by self-sustaining I take fully independent from Earth supply chain for absolutely everything. A civilization that could continue existing without single delivery for Earth.
It's Mars but with training wheels, since if there are problems stuff can be sent to/from the earth at any time as opposed to waiting for a transit window to open. With water ice in Shackleton Crater at the South Pole a permanent base should be very feasible with today's technology plus an operational Starship.