Why is Clean Code suggesting avoiding protected variables?

I just learned about the existence of this book a few minutes before seeing this post (what's the name of the phenomena whereby after discovering something once, you immediately observe it again?), and the M.O. of the book resonates with me; I do lots of refactoring, as well as a fair amount of API design, and I've always put a lot of thought into the "best" way to write code. E.g. while I personally enjoy writing clever code, such code is usually a detriment in a team environment. I also get irritated when others don't put time & effort into writing clean code (or at least putting a minimal amount of thought and effort into it).

But I see that there's some pushback against this book, and so I'm not sure if it's all that it's cracked up to be. Anyone have any opinions?

Actually the perspective of languages like objective C and Python about variable privacy or accessibility is pretty flexible.