Being able to install software without needing an OK from the hardware manufacturer has been standard for over 40 years now. People do it on Windows PCs, on Linux PCs, on MacBooks and on Android phones, and that very clearly has not caused the extinction of the dinosaurs yet :)
The document Apple has published to me reads like it's written by a 5 year old that just was served too many sweets shortly before bed time.
IMHO this is about revenge, not about platform security.