If the manufacturer makes parts easily available, wouldn't the incentive to steal devices to sell for parts more or less disappear? Same thing with counterfeit parts. The market for stolen/fake parts exists because OEM parts are essentially impossible to acquire legally.

Serialisation is simply another way for Apple to maintain control. You can now repair a device, but only with Apple's blessing and knowledge. The privacy/safety stories they sell are just that.

An iPhone-quality OLED display is always going to cost $150+ new as part. That alone is enough value to steal a phone for parts.

Personally, serialization that alerts the user "you have unauthorized parts, if your battery catches on fire or your screen has crappy colors it's not our fault" -> this is good, I am in favor of this, serialization that disables the device or features -> bad.

The part would have to be easily available and cheap.