Disclaimer: I am biased. I've talked to some of the people on the team. And am friends with one of the many people who've worked on the project.

So a few points here;

First, a lot of people are pointing to the JWST as the heir apparent, but that's not quite correct nor true. SOFIA is the only observatory that looks at the Far Infrared wavelength, the only one on Earth. The rest are in LEO. There are some who will say that it's not valuable, but the truth is that we don't know if it's valuable or not. We've only been doing these observations since 1983 with a handful of telescopes (the first one was the Infrared Astronomical Satellite or IRAS, IIRC).

However, we've already made significant finds, including water vapor on Ceres and observations of the galactic center + stellar nurseries.

Second, you can't change a space telescope without a Shuttle-style mission, but you can endlessly tool and re-tool SOFIA. What this means is that SOFIA can adapt to different observation targets and we can try new technologies on board.

Third, SOFIA can image wider sections of the sky, whereas JWST is great at looking at particular targets/regions. More technically, they have completely different fields of view from the specs;

SI Fields of View

SOFIA: HAWC+ > ~10 arcm2
JWST: < 10 arcm2 per SI

We don't know what's out there. Or, to put it in a more Rumsfeldian fashion, we don't know what we don't know, and it is important to do wider surveys. SOFIA is the only Far Infrared telescope in the world with such a wide field of view.

Fourth, it is absurd to me that we're arguing if we need a telescope. It's like arguing that a single camera is enough for a family. Why shouldn't we capture more of our universe in a world filled with sensors? And peer ever deeper into creation?

The more of these instruments we have, the greater the number of people who have the opportunity to point it at something and discover something new.

More directly; I don't think scientists should spend most of their time writing and judging applications for a limited number of spots on observatories. I think they should spend most of their time doing actual science. The greater the number of capable observatories that are out there in the world, the observation time there is to go around, allowing for newer/riskier ideas to be tried.

Fifth, I struggle to articulate this point, but we keep removing assets instead of adding capabilities when it comes to NASA. A great example of this is the loss of Arecibo. Or the loss of the ability to bring large payloads back down from orbit. This obsession with getting the most science per dollar is understandable and desirable, but pursuing it by removing capabilities from our toolbox is suboptimal.

Could you imagine if any country ran a military in the same way? Getting rid of amphibian assault capabilities because you have parachute regiments doesn't make sense.

Each new capability adds to the whole, making something greater than the sum of its parts. Here's an example that I have lifted from a slide that's a part of a presentation that was given by a SOFIA project scientist and the PI for the JWST's MIRI + NIRCam, Tom Greene, in 2017,

Let's say we wish to understand and image gas and shocks in protostellar jets. We need to image at multiple wavelengths to capture all of the processes at play.

There are so many processes going on here that really can't answer "simple" questions like, "how is energy transferred from accretion disks to the jets of young stars?" or "How does this relate/feedback into the molecular disks where stars are formed?"

We can imagine a scenario where SOFIA spots a protostellar jet, we re-tool it to get a better look at particular wavelengths, hand it over to JWST + Hubble to image the protostellar jet, and add in observatories across the world. And then, we can use all of this data to construct a richer picture of these processes.

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Please call your congressperson and ask them to fund more science. After all, of what use is a baby?