Analysis of information sources in references of the Wikipedia article "GNU Free Documentation License" in English language version.
FSF, a Free Software organization, isn't being entirely true to the Free Software ethos while it is promoting a license that allows invariant sections to be applied to anything but the license text and attribution. FSF is not Creative Commons:the documentation that FSF handles is an essential component of FSF's Free Software, and should be treated as such. In that light, the GFDL isn't consistent with the ethos that FSF has promoted for 19 years.
It is not possible to borrow text from a GFDL'd manual and incorporate it in any free software program whatsoever. This is not a mere license incompatibility. It's not just that the GFDL is incompatible with this or that free software license: it's that it is fundamentally incompatible with any free software license whatsoever. So if you write a new program, and you have no commitments at all about what license you want to use, saving only that it be a free license, you cannot include GFDL'd text. The GNU FDL, as it stands today, does not meet the Debian Free Software Guidelines. There are significant problems with the license, as detailed above; and, as such, we cannot accept works licensed under the GNU FDL into our distribution.
With the transition, the Wikipedia community will now be allowed to import CC-BY-SA text from external sources into articles. If you do this, the origin of the material and its license should be explicitly noted in the edit summary. If the source text is dual- or multi-licensed, it is only necessary that at least one of the licenses is compatible with CC-BY-SA. It is not necessary that external content be dual licensed under the GFDL.