Good essay, though perhaps "user" has some of the problems we have when taking about "content" (e.g. art, music, movies) and "consumers" of it in that it automatically places the thing we're talking about in a narrow box. Someone who practices the freedom to change software is surely a developer— in the language of people-in-boxes— not a user. Why care about user's freedom to do something they don't do by definition?
I guess that talking about 'freedom' without great care runs into the problem that suggesting to someone that they are being oppressed is a quite uphill battle: (imagine a Monty python sketch) "See here! you're being oppressed!" "Uh. No I'm not" "Yes you are!" "If _I_ were being oppressed you can be sure I'd already know it!" "No sir, you can only be free if you stand on one leg!" "One leg you say? Well that doesn't sound free at all! It sounds bloody inconvenient!" "maybe a little, but if you use both then you have to buy two shoes!" "but everyone buys two shoes!" "now you see how insidious the oppression is!" […]
I wonder if more effective when we talk about abstract freedom in terms of what _other people_ should have a right to while the _personal_ discussion should center more on the concrete things they can and can't do ('Can you change the OS on your computer?', 'can a third party evaluate this system for spyware?'). Though maybe I'm falling into the trap of 'open source'— but I don't think so, I suggest this not because of any discomfort in talking about freedom, but rather because people just seem unwilling to believe they don't have it ("I'm quite free, I can facetime with any Apple approved device I want!") but more willing to believe that other people are being deprived it.
On further contemplation I wonder if my suggestion that there be a name for secureboot-freedom-as-a-feature isn't actually a bad one. The line between a restriction and a missing functionality can be blurry to people: Many people seem unaware of restrictions on their ebook devices because without an obvious copy button that tells them "no" the inability to copy just seems like one of an infinite number of benignly non-implemented features. Promoting freedom as a feature runs the risk of making non-freedom sound like a regrettable but perhaps forgivable omission rather than a hostile act of control.