Hm, while I completely agree about not wanting proprietary garbage on my machine, I'm not sure about this logic. A third party can stipulate anything it likes,

Hm, while I completely agree about not wanting proprietary garbage on my machine, I'm not sure about this logic. A third party can stipulate anything it likes, in order to use their service - you're always free not to use that service. Arguably, the ability to certify that you, the user, are indeed running the code you say you are is a feature provided to you, rather than a restriction imposed upon you. Not a feature I have interest in using, but nevertheless it's possible to frame it that way around. The fact that such code tends to be proprietary is (again, very arguably) besides the point.