It's not about "doing a disservice", it's about obeying the licence terms.
The GNU Free Documentation Licence has (optional) clauses in it ("invariant sections") which preclude making modifications to certain parts of the documentation, which makes it effectively non-free. While some manuals licensed under the terms of the GFDL are entirely free, several of the major GNU projects have large political rants embedded within them, which can't be altered.
I can see both points of view here. If you write opinion pieces you might not want your opinion altering and republishing without your consent. However, I would also argue that a free software technical manual might not be the best place to put such opinion pieces, because there is a certain hypocritical aspect to championing free software rights, but not applying the same principles to the documentation of the same. It would not be difficult to keep the twain separate.
Full disclosure: I voted against keeping GFDL documentation with invariant sections in the Debian archive back when I was a Debian developer. This is because one of the primary benefits of free software is that everyone has the same rights and responsibilities as everyone else. Distributors and end users have the same rights to distribute and modify as do the original maintainers (albeit they can't relicense under different terms). The GFDL invariant sections make one organisation or individual "more equal" than others, and that's against the entire spirit of what free software is all about. This is one instance where I think RMS really dropped the ball. I might not agree with all of his philosophy but it's usually well thought out, and in this case I think it's not well thought out at all.
Debian has the Debian Free Software Guidelines, upon which the OSI Open Source Definition is based. If you read them, you'll see that the GFDL with invariant sections fails the clause regarding "modification and derived works". Because it explicitly restricts your ability to modify and distribute.
Trisquel may have a different interpretation. I understand they are closely aligned with the FSF, so may not agree with the Debian stance.
This is one point upon which I do think the FSF is entirely wrong. Putting invariant sections into the GFDL made the licence firstly overly complex, and secondly made it incompatible with the OSI and DFSG interpretation of freedom. All just so they could include immutable political content in their documentation. The fallout from this made it a very poor choice to use for documentation, and was a spectacular own goal. If you follow the licence to the letter, it means you can't embed source code examples without being required to also include the invariant sections (you aren't permitted to delete them). This makes the licence impractical to comply with for a lot of common use cases. Overall, it's simpler to ignore the licence entirely and simply use the same licence as used by the rest of a given project's codebase. I did use the GFDL in a few projects at the time of its creation, but no longer do so after getting a better understanding of it. It's a bad licence.
The GNU Free Documentation Licence has (optional) clauses in it ("invariant sections") which preclude making modifications to certain parts of the documentation, which makes it effectively non-free. While some manuals licensed under the terms of the GFDL are entirely free, several of the major GNU projects have large political rants embedded within them, which can't be altered.
I can see both points of view here. If you write opinion pieces you might not want your opinion altering and republishing without your consent. However, I would also argue that a free software technical manual might not be the best place to put such opinion pieces, because there is a certain hypocritical aspect to championing free software rights, but not applying the same principles to the documentation of the same. It would not be difficult to keep the twain separate.
Full disclosure: I voted against keeping GFDL documentation with invariant sections in the Debian archive back when I was a Debian developer. This is because one of the primary benefits of free software is that everyone has the same rights and responsibilities as everyone else. Distributors and end users have the same rights to distribute and modify as do the original maintainers (albeit they can't relicense under different terms). The GFDL invariant sections make one organisation or individual "more equal" than others, and that's against the entire spirit of what free software is all about. This is one instance where I think RMS really dropped the ball. I might not agree with all of his philosophy but it's usually well thought out, and in this case I think it's not well thought out at all.