I bought a soda charger a while back and it requires a specific brand of c02 cartridges. Is that considered illegal? Are there all kinds of companies out there manufacturing generic Touch ID sensors/home buttons? If there are I'd love to know who those manufacturers are. I know I wouldn't want my home button/Touch ID sensor replaced with something different than what Apple uses.
Initially no, it would not be illegal because the cartridge could have a unique shape. If an alternate manufacturer either creates new cartridges with the same functionality and shape, or recycles cartridges from the creator of your soda charger, then it can be illegal. There are steps involved to prove illegality.
I don't know if there's a generic home button manufacturer, but we don't know if the replacement home button was generic. People are assuming it was. To base the premise of your point on that assumption is foundationally unsound. It could have been re-used from another iPhone. That would make it 100% OEM. In this case it wouldn't have mattered. From what I've gathered it wouldn't matter. Replacement or OEM is immaterial to Error-53. It the validation that's important. That validation is home button A on iPhone A is tied to Secure Enclave A. If I replace home button A with home button B on iPhone A there will be an invalid connection with SE A. Bricked iPhone.
Focusing on the replacement home button is a rabbit hole to nowhere. It didn't brick the phone and Error-53 didn't act as a security wall in that instance. The guys phone worked fine for approx. 4 months.
In my opinion, this would have never been a problem if Apple did the following:
-Caused Touch ID to be inoperable when the replacement part was installed.
-Pop up notifying customer unauthorized part detected which disables Touch ID. Contact Apple for support.
-Leave the rest of the phone alone.
Bricking a customer's phone because of an optional feature should not have even been within the realm of possibility. You've asked how many people this has affected. I guarantee it's affected more people than there have been compromised Touch ID access. Afaik, that particular number is 0.