The consumer can decide if they wanna risk calibration variation or 'spoofed or something like that' parts vs. not having a functioning device at all or paying a premium to let Apple deal with it.
I expect one of Apple's fears is that most "consumers" have nothing like the technical background us here on the forum do and if they get their device repaired at a third-party they will assume that it used "genuine Apple parts" and if there is an issue with that repair, will not complain to the place they got the repair, but will go on social media and complain about "Apple's crap product".
I believe preventing using non-new OEM parts for critical security functionality, but allowing them for other functions is a good baseline to both expand repair options and to (hopefully) reduce repair costs. I also like the "parts history" so that if you encounter an issue with having a "non-OEM" part being used and taking it to Apple, Apple can educate you on what happened so the consumer becomes educated that their previous repair was not correctly done and it would help Apple identify what is causing the problem.