You are not.
It's certainly convenient in this modern world to pay for and use one of their devices though.
Considering market forces are against it, I believe the only practical way to accomplish this in the long term is for this to be a right that is enforced by legislation. I don't think it is even far from precedent surrounding first sale doctrine and things like Magnuson-Moss, that the user should be the ultimate one in control post-purchase, it just takes a different shape when we're talking about computing technology.
Limitations because it's not just protection - you don't get to choose which authorities you trust. Defaulting to manufacturer/OS vendor as the default authority would be ok, but there is no option to choose. Users have no power over their own device. That's not ok even if most choose to never execute it or don't know about it, it will lead to abuse of power.
No one is forcing you to buy a particular device.
True. But society in practice requires a smartphone with one of two operating systems to live a normal life without significant efficiency losses in your day. Now all phones with both of those will be completely walled off. You'll be forced to participate or make your life a lot less convenient.
Surely you wouldn't defend absolutely anything happening to say roads just because you're not forced to drive, technically speaking?
Furthermore, if you fundamentally allow this behaviour, the market forces are sure to push us to an end state where users simply have no control, and there are no viable alternatives. We are most of the way there already when it comes to smartphones. The cost of entry to this market (many $billions over many years, if you can even manage to gain meaningful marketshare at all), and the amount of money that is on the table (30% of the $billions transacted on a successful platform today, but who knows how far they push with a real stranglehold) means that it is virtually impossible for competition to solve this problem.