The sensor IS PART of THE CHAIN OF TRUST, whether you use the sensor OR NOT, the hardware INSIDE IT is checked on boot (and at other times) and if it doesn't marry up to a trusted value, it's kicked out.
People, take a week off whining (and a LOT of load off the internet!) and study THIS document, and then come back if and WHEN you understand it:
https://www.apple.com/business/docs/iOS_Security_Guide.pdf
If not, shush, and leave it to people WHO UNDERSTAND.
Then it's a fundamental design flaw. Fact: the home button's use as a fingerprint sensor is 100% arbitrary. If I've never set it up as a security check point to access my phone, never setup or used Apple Pay, if the home button is or was only ever used as a home button, then it shouldn't be held against me if I choose to have it repaired via third party. There is zero security risk involved but thanks for your cool pdf and the douchey condescending tone, dork.