One position is "if it's not ultimately free, dismiss it." (And some count FDL as *non*free.) I rather support "make it as free as possible. Then keep improving."
GFDL is free by all measures if you don't use invariant sections and so forth, isn't it? Does anyone dispute that? (I know Debian wouldn't accept it with invariant sections.)
A document licensed under the GFDL with invariant section is still free, what it isn't though is free software; but it is free documentation.