I don't even think it should have to be justified. Booting from external media is one of the most basic computer maintenance tools we have. It's not like the computing industry has been giving two shits about user freedom anyway. The cynic in me wants to say that the insecurity of modern computing was intentional, so as to eventually require such user-hostile lockdowns. However, the rationalist in me understands that it most likely just ended up happening this way by chance. Either way, it's unfortunate that everything is being locked down more and more in the name of security. At the very least, such walled gardens should be opt out.