Honestly, publishers should just allow it. If the concern is lost traffic, it could be worse — the “source” link in the summary is still above all the other results on the page. If the concern is misinformation, that’s another issue but could hopefully be solved by rewriting content, submitting accuracy reports, etc.
I do think Google needs to allow publishers to opt out of AI summary without also opting out of all “snippets” (although those have the same problem of cannibalizing clicks, so presumably if you’re worried about it for the AI summary then you should be worried about it for any other snippet too).