The problem with LaTeX and Debian was roughly as follows: the LaTeX people wanted to let end-users know when they were running a modified version of LaTeX or of a LaTeX-package, so (by running an unmodified version) end-users would be guaranteed to have the same rendering of a document on different machines. Debian wants LaTeX and LaTeX-packages to be free, so users could modify and distribute modified version at will.
So, where is the problem? Well, really there is none - the only thing that has to happen is that a modified version must somehow say it is modified (or not say it is unmodified). The formulation of the LPPL was problematic and the Debian and LaTeX people have been working very hard to resolve this problem.
Actually, there seems to be consensus on debian-legal that a document released under the GFDL without invariant sections is indeed free. However, if you want your document to be available under a free licence, then the GFDL without invariant sections might not be a good idea. The reason is that someone else could add something interesting to your document (good) together with some invariant section (annoying). Now you, the original author, are not allowed to use the addition without also incorporating the invariant section.
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The problem with LaTeX and Debian was roughly as follows: the LaTeX people wanted to let end-users know when they were running a modified version of LaTeX or of a LaTeX-package, so (by running an unmodified version) end-users would be guaranteed to have the same rendering of a document on different machines. Debian wants LaTeX and LaTeX-packages to be free, so users could modify and distribute modified version at will.
So, where is the problem? Well, really there is none - the only thing that has to happen is that a modified version must somehow say it is modified (or not say it is unmodified). The formulation of the LPPL was problematic and the Debian and LaTeX people have been working very hard to resolve this problem.
Actually, there seems to be consensus on debian-legal that a document released under the GFDL without invariant sections is indeed free.
However, if you want your document to be available under a free licence, then the GFDL without invariant sections might not be a good idea. The reason is that someone else could add something interesting to your document (good) together with some invariant section (annoying). Now you, the original author, are not allowed to use the addition without also incorporating the invariant section.