It either works reliably or it doesn't; if it doesn't, it's better that everybody be clear about that.

Fair enough. While I would kind of wish AI could be reliably detected, deep down I know this is impossible and it would be pretty bad if we had, say, a prosecution that succeeded because "this 'provably-non-AI' photo places you at the scene of the crime" because only a few underground people know how to remove a watermark.

Not necessarily. Knowing an image for sure is fake has value, even if you can’t guarantee the reverse is true.