People repair their brakes wrong all the time. It’s absolutely caused accidents.
It also allows end users to install parts superior to OEM, improving braking capabilities, and preventing accidents.
Any automotive technician can tell you that manufacturers take engineering shortcuts, resulting in a product with certain deficiencies. The manufacturer’s motivation is to put out a product that widely appeals to the general public. They want nothing to do with a product specifically tailored to the needs of a particular individual.
I’m glad you mentioned insulin pumps, because there is a community of developers working on pumps, making them available to a broader audience, providing more people with better control over their blood sugar levels than manufacturers are willing or able to provide on their own.
https://openaps.org/
What you are arguing for is a threat to systems like OpenAPS, and to the people who benefit from them.