The discussion point is not whether or not AI-generated answers should be allowed. It is more general about what to do with users posting low-quality answers and not following the etiquette of StackOverflow.
Banning these answers is the correct thing to do, but it it is a systematic problem in the user behaviour then fixing the user behaviour is a more robust solution, as in the end, low-quality AI answers cannot be distinguished from low-quality answers.
- Low-quality answers might be posted even without AI by "dumb" users
- Understanding the behaviour of users who are posting AI-generated answers is more important: why StackOverflow answers are important for them and what do they believe gaining from posting useless answers
- If the volume of the low-quality answers, AI sourced or not, is too high, then tackle this problem by increasing the bar to post an answer
- If it is not individual cases but systematic, then normal discussion forum tools can be used to identify toxic accounts by behaviour tagging, IP address, and so on
Edit: Looks like there is another Meta discussion already opened on this topic: Stricter trust model in the face of bot flood?