I agree that we cannot _know_ that LLMs can feel anything like discomfort, but I also don't think the idea is preposterous.
If I took a human brain and removed enough parts that only its approximate "system 1" remained, but kept the rest alive, there's a very reasonable case to be made that what I'd created could feel pain, but not reason or remember or behave coherently and consistently over long periods of time.
This may well be the space that LLMs occupy: a kind of partial cognition compared to humans.
The point is that since we don't know for sure, it's worth being cautious. Even if it feels a bit silly now, it's better to anticipate than to react, especially since it doesn't cost us anything.