So first off, putting something in mask ROM[0] does not make it equivalent to a circuit. Circuits cannot be copyrighted[1] but mask ROM programs can be; meaning the latter is just as non-Free as rewritable software. It is legally silly to distinguish between read-only and rewritable software, even if it might have a small engineering upside of prohibiting the imposition of new antifeatures.

That doesn't mean that mask ROM is free of antifeatures, though - in fact, often times mask ROM is the highest privilege level in the system and thus the best place to put antifeatures. In the case of x86 PCs, the BIOS gets it's own privilege level above the kernel; ARM PSCI also runs in EL3 above normal kernels or hypervisors. These can still actively damage user freedom even if it's "technically hardware" and non-updatable.

Also, the fact that it's not rewritable means that...

1. Security bugs[2] will never be fixed[3], rendering the hardware unsafe to use over time.

2. We cannot practically replace the firmware with a Free equivalent.

It should not be understated that the vast, vast majority of hardware did not come Free. We had to open it ourselves through painstaking reverse-engineering and reimplementation work. This is an ongoing burden that the community must meet for the foreseeable future. Manufacturers are not going to stop shipping hardware with proprietary firmware or drivers anytime soon. Ergo, anything that stands in the way of firmware or driver reimplementation is, in my opinion, bad. This includes making it more difficult to update or replace firmware by putting it into a mask ROM.

My personal opinion is that you can't really draw a line in the sand and say, "this hardware respects your Freedom, but this other hardware doesn't". Hardware manufacturers have zero interest in fully-Free firmware, and I don't expect this to ever change. Not even with RISC-V, which will almost certainly have even more "embedded" fragmentation than ARM does. Whatever standard the FSF writes for "Respects Your Freedom" hardware, someone is going to try and rules-lawyer non-Free software into getting that badge. So they should not provide a strict standard at all.

There's also another question of how much energy we actually want to burn on getting Free firmware into chips. An alternate interpretation of the idea behind the Free BIOS campaign is that the BIOS itself got "interesting" enough to be a Freedom threat. Back when it was still a ROM, Free kernels could ignore it entirely; now it gets it's own privilege level and has to at least be considered. CPU microcode is less of a threat than the BIOS, here - the microcode just lets you patch how certain instructions get decoded, while the BIOS can actively debug and spy on Linux.

[0] I am going to use the term "mask ROM" loosely. Consider one-time programmable memories like PROM or EPROM to be in the same category, as they cannot be electronically erased and then reprogrammed by the same circuit that uses them.

[1] There is a sui generis right for "mask works", but it is far less toxic than software copyright. For one, it has a reasonable term length.

[2] I am assuming security from the standpoint of an end-user, of course. Being able to defeat TiVoization is not a security bug for me.

[3] It is possible to swap ROM chips in some cases, if the part is socketed, or if it is soldered and the user has the appropriate level of soldering skill. However, at this point this is no longer read-only. It's just Flash memory with extra steps. There is no legal or ethical difference between reflashing a chip with proprietary software on it and replacing it with a new chip with new, proprietary software on it.