A huge fight looms over the NASA budget this fall

Respectfully, if you claim you have not seen any justification for SLS and Lunar Gateway, then you either haven't been looking very hard, or are instead conflating "rejecting arguments" with "no justification".

While neither the SLS or Lunar Gateway are the most efficient path to achieving a permanent Lunar Presence on the Moon, they certainly both fulfill a number of objectives:

First, SLS. Yes, it's not efficient, yes it's billions over budget, but there are a number of reasons it's absolutely imperative it remains funded until at least Artemis 4:

1. Crucially, SLS is the fastest way to get crews to the Moon. Starship is exploding more than ever and we have no idea when it will actually be ready. SpaceX has missed all it's projected timelines already. New Glenn has launched once and then delayed massively test launch 2. SLS has continued to have problems but they appear to be solved (for now), and so there's nothing even close to SLS for getting us to the Moon.
2. Running a staged approach where we utilize the technology and budget we have now to start doing Lunar work and therefore have more accurate data to inform future technology (like starship) is a much more reliable path towards consistent Lunar access than cutting every arguably inefficient program and hoping one of our hail-mary technologies pays off. Especially when there are serious geopolitical concerns that China will be able to get to the Moon first, dominate the location, and set all the geopolitical rules there.

For Gateway:

1. We have the ISS, but we have not deployed a space station anywhere else - especially not somewhere outside of Earth orbit. This will be a massive science and logistics learning opportunity to get it running.
2. Likewise, learning about human habitation in deep space (depending on your definition of Deep Space - we'll be much further outside of the Earth's magnetosphere and thus exposed to much more radiation) will be a massive science and technology boon from Gateway.
3. Although its orbit doesn't result in consistent access to the South Pole, it still will be a reliable back-up station for managing the unavoidable problems that will arise on the Lunar surface. Having multiple failure points in your chain back to Earth can only help.

For both:

1. Even if you discount all of the above, developing both programs as "pork" are massive training and technology opportunities for a global group of friendly space agencies and companies. We are having to train a new generation of scientists and engineers to re-learn how to do what the Apollo generation did. This is no small feat as that entire generation has either passed or retired. The institutional knowledge is gone. Moreover, many of these technologies can be re-applied on Earth. For instance, the NASA Technology Transfer Program explicitly licenses NASA patents for commercial use on Earth.
2. Globally, these cancellations represent yet another Trump Admin self-inflicted wound to the standing of USA. The Artemis missions involve billions invested from allied nations - ESA has already built the damn Orion capsule to sit on top of SLS, Canada has spent billions on Canadarm-3 + other support systems for Gateway. Cancelling these programs outright is going to piss off these partners and make them much much more unlikely to commit to supporting the Artemis programs.

I could go on, but I think I've more than made my point for a Tildes comment. In my view as someone who works on Lunar stuff, maintaining this funding is an unequivocal win for the Lunar community. We are well past the time when cancelling either program would be helpful.