Security is about trust. If you trust Apple or Google, and don't care about their 30% tax, then you should be able to choose that. Make it the default, even. But if you don't trust them, and don't want them to control what runs, that should be your choice too. It's your device for fucks sake!
"Security" is a weak argument for unconditionally giving up all control over your own device. Especially when that control is very obviously being used against us by those very same that are claiming to protect us. The situation is reminiscent of countless dystopian novels. If we're going to accept that anyway, I think it needs to come with much stronger protections for the common good in other ways than vague and pretty bogus "security" arguments. If they want lock in, I think they should have to operate the platform on a cost basis, and with strong antitrust protection in exchange for that privilege.
Most Windows PCs allow users to enroll keys in their secure boot system. Do you hear about grandpa getting his life savings stolen by this mechanism often? I certainly haven't. Much more likely he lost it to social engineering, where no technological measure is going to help you.