Apple doesn't allow downgrading (and it's gotten even harder with Touch/Face ID not being downgradable with SHSH blobs), so people accidentally update, or get their hardware replaced in a repair, are SOL.
Users that care about having control over their devices shouldn't be buying Apple hardware in the first place. Not that I support Apple's anti-consumer practices, but if you buy one of their products, you have to know what you're getting yourself into.