I think there's a lot of confirmation bias in this thread coming from two groups: anti-AI activists and cathedral-development proponents. They take what was written at face value and use it to further their narratives that AI is ruining the world and "social coding" is unsustainable, respectively.
What the Ladybird maintainers did here was messy and a punch in the gut to actual contributors who liked the project and the openness of it. There was no effort to shore things up, just a boilerplate message from a maintainer account then closing of your PR. Of course, Ladybird maintainers have no obligation to outside contributors but it shows a lack of grace nonetheless.
Reading between the lines, there seems to have been a stark shift in attitude from Andreas which is concerning. Ladybird started from SerenityOS (a hobby OS) and he always encouraged everyone to submit a patch. Sure, LLMs have increased the amount of slop PRs, but I feel like those are easy to spot and close accordingly. I don't have links handy, but maintainers would point to a section about AI usage in their CONTRIBUTING.md then close the PR whenever obvious slop was submitted. This idea that people "own" the code they contribute is strange to me; the code would be determined worthy of acceptance at review time, why does someone have to "own" it?
All that is to say: I think there's much darker things going on here and AI+security is a nice scapegoat. Time will tell, but this reeks of a rugpull in the future. Disappointing day.