People who oppose the use of LLMs have the right to do what they want with their software just like anyone else does. It’s not “childish” or “toxic” for them to express their opinion by changing the license on their own software or writing about it on their own blog.
Furthermore, if the GPL is really as unenforceable as you say, then there’s no reason why their license change is “punitive”. Either the GPL works, in which case the Asahi Linux maintainers have the right to restrict use of their software, or it doesn’t and there’s no reason why anyone should be upset by a gesture of free speech.
The Asahi Linux maintainers have the opinion that LLMs are harming their ecosystem, and if they want to prevent people from using LLMs on their software, then they should be able to do so without being unfairly attacked.