"This is not any more difficult than policing licensing terms is today. "
It significantly more difficult that policing licensing terms. Any act that would break licensing terms is an act that is necessarily done publicly. While there would be dispute about whether the act violates a license, it would be easy to reach consensus that the act took place. E.g. in a questions of incompatible licenses, there may be argument over whether a submission's license in compatible with the projects it would be plainly visible to all what license it was submitted with.
Using an AI tool is done privately, so there would be a lot of allegations that cannot be connected to evidence. Compare to accusations of text with em-dashes having been AI-generated, with the writers protesting that they've used em-dashes all along.
"It should be about spelling out the rules, then banishing people who break them"
Rules that can only be poorly enforced become rules that are arbitrarily enforced, which in turn erodes respect for the system of rules as a whole.