Debian's kernel is deblobbed and contains only free software. If you can find an example contrary to this, it is a bug.
The poster on the thread you linked is making the argument that free software shouldn't be looking for non-free firmware, even when it isn't installed. That's... interesting and not something I've ever heard complained about.
The FSF doesn't endorse Debian because of the non-free repository which, while not officially a part of Debian, they consider a Debian. If you install only the "main" repository you will get only free software. The default install only contains the "main" repository.
It has long been the case that FSF-endorsed distros could not use the Debian kernel, even though it contains only free software.
It had always been my understanding that the intention is that the messages the Debian kernel displays looks like an error
message suggesting that the module should have been present. Even if
it looks less like an error, and is more matter-of-factly "such and
such functionality is disabled because nonfree.bin could not be
loaded"; reading between the lines, that sounds a lot like "install
nonfree.bin for that functionality".
However, following the more recent discussion, particularly the comments of Alexandre Oliva (the Linux-libre maintainer), I'm not so sure. I hadn't realized that many of the extreme deblobbing measures (replacing firmare filenames with "/* DEBLOBBED /") in Linux-libre were because it must not load non-free blobs even on distros that are hostile to that goal. On FSF-endorsed distros that are not hostile to that goal, what measures are* necessary?
Ironically, many GNU manuals are included in the non-free sections because Debian considers the GNU FDL non-free because it allows invariant sections - sections that cannot be changed.
