Apple expended a significant amount of resources designing this bespoke boot chain so that it isn't locked down and does in fact let users run completely unsign

Apple expended a significant amount of resources designing this bespoke boot chain so that it isn't locked down and does in fact let users run completely unsigned operating systems (as long as they have physical access and give consent with their local user credentials). In fact, the design goes further, allowing individual installed OSes to have different security levels, thus allowing users to get the benefits of both a completely opened up OS install and a fully Apple-vetted, secureboot install. They aren't going to backtrack on all that. That'd be silly. So please stop the FUD about Apple locking their devices down; this is a Mac, not an iPhone :-)