I agree, and I think there's a compromise. Allow the pairing of harvested parts, but also allow users to report their unit as "stolen" so the parts can't be paired.

However, this is probably fraught with problems that Apple doesn't want to deal with. Users will want to know if someone tried to pair their parts and they'll be hit with a large number of subpoenas daily from people who want to know which repair shops had their stolen phones.