If you're doing free-all-the-stuff for principle, I think it gets un-comfy drawing the line at stuff that runs on x86 and ARM ('specially as your monitor probably has an ARM in it anyway). If you're doing it for security, I think you must strive for peripheral openness too, or you're mostly wasting your time.
I believe computing freedom is a right people should assert, and I should inform them why they should assert it, but I don't go as far as saying it's unethical to use non-free devices and/or software. At least not when non-free is more readily available and, from the perspective of the average user, more "convenient" than free.
Personally, I like Debian because it removes non-free blobs from the kernel (and I check the license on a package before I install it). But let's say Ubuntu was the only available GNU+Linux distribution. I would still choose it over Windows or MacOS because mostly free is better than completely non-free, and I would rather support Ubuntu (or Android, for that matter) than enable and give money to Microsoft or Apple.
As for peripherals, from a practical point of view, doesn't the type of peripheral matter? A monitor or printer (output devices) going rogue seem far less dangerous than a rogue webcam, for example.
Personally, I don't really care at all about RMS's weird definition of freedom and I use what's best for accomplishing my goals. But drawing arbitrary lines of "freedom" has always made even less sense to me.
Thunderbolt devices have to be approved before they can be used.
http://dxg49ziwjgkgt.cloudfront.net/wp-content/uploads/2016/...
http://dxg49ziwjgkgt.cloudfront.net/wp-content/uploads/2016/...
