I completely understand your comment, it's reasonable to want sources. I didn't have enough time when I made my original comment to do some good sourcing, but I had that time now. In the interest of not making this comment absurdly long and not repeating work that's already been done, I'll try to be brief and link to secondary sources that contain accurate analysis where possible, rather than linking to primary sources with mostly my own analysis.
>but without considering the second-order effects on his credibility and funding if he actually turns out to be proven substantially wrong in the future
He has continuously made predictions about how bad deep learning is and how it would never achieve much, unlike his "much better" neurosymbolic theories that have never shown results anywhere near as significant (there might be good ideas there, doesn't mean that his continuous goalpost shifting is good science). Those predictions have continuously been proven wrong for the last decade, including a number of predictions specifically about LLMs. This is relatively normal in the academy, people have hobby horses, but he's now engaging in public discourse and advocacy about an actually contentious topic and there are different standards here, so I'm going to respond in that context. If you're not familiar with him at all, that's fine, here's some of his track record and explanations of why he's wrong:
For deep learning in general, in case you want an overview of where he's coming from (he stands by everything in this article today, don't let the age inspire sympathy, he's a deep learning skeptic to the core): https://www.newyorker.com/news/news-desk/is-deep-learning-a-...
For GPT-2 (a moderately important retrospective is in the comments): https://www.lesswrong.com/posts/ZFtesgbY9XwtqqyZ5/human-psyc...
For GPT-3: https://www.tumblr.com/nostalgebraist/628024664310136832/gar...
CTRL-F "Gary Marcus" on this page to find a bunch of sourced, specific claims from Marcus alongside evidence they are wrong: https://gwern.net/gpt-3-nonfiction
He has never stopped, and probably never will. He's the student of the original guy who first buried neural nets back in the sixties or seventies; he's royalty in symbolic AI. The only concession I've ever seen him make to the continued progress of deep learning and LLMs in spite of his continuous early proclamations of death is, bizzarely, that he is concerned about existential risk from current AI research. I don't personally see how he squares "Deep learning and LLMs are all nonsense, have hit a wall, off-ramp on the road to AGI" with "Current AI research [which is overwhelmingly deep learning, even if he doesn't say that part out loud] presents an existential risk", but he does it somehow.
Basically, no matter what new AI research or artifacts come out, if they are made with neural nets he will explain:
1. They are not that important
2. It's a dead end
3. They're harmful because people might wrongly get the impression that they work
4. They're nowhere near as good as his favoured AI architectures are, if only his favoured theories had as much funding as that broken deep learning crap