If you choose not to use non-free firmware, even when it means that many hardware devices are unusable for you, that's fine. I can understand why you would take this position. From what I understand, Richard Stallman practices what he preaches, and has a computer with no BIOS, no hardware that loads firmware, and no microcode running on the CPU.
What isn't fine is calling Linux "open core" just because it supports certain pieces of hardware that operate this way. "Open core" is a specific business model based on keeping part of the code proprietary and forcing users to pay you for its use. Simply interoperating with existing closed-source devices or code doesn't make something
By using the term this way, the FSF is diluting its meaning. People who really do have open core business models will now point to their press release and say "look! The Linux kernel is open core too! So our business model is fine." As usual for the FSF: ready, fire, aim.
What also isn't fine is blasting people working on open source software because their computers have BIOSes, contain hardware devices that need microcode, and have modern CPUs.