Specifically, "A free system distribution must not steer users towards obtaining any nonfree information for practical use, or encourage them to do so."
This is a political stance based on rational arguments and has nothing to do with religion.
And by Debian's definition, some of FSF's own packages are non-free (notably, the documentation), so you have to explicitly opt-in to installing that.
I wish both of them directed their efforts towards more pragmatic problems, like making their software more accessible. In the rest of the world, freedom is usually a function of accessibility.
Political views have parties and parties have supporters. FSF is more like a cult that has followers.
How else do you explain their rejection to include Debian as a fully free distro?