Also, if I'm not mistaken, even Debian's "main" repository has some GNU FSDG
issues, so even if one manages to "do it yourself" the process of disabling
the other repositories, you still end up with possibly non-free software.
https://www.gnu.org/distros/common-distros.html says:
Debian conscientiously keeps nonfree software out of the official Debian
system.
Is that statement is wrong? However, you may be referring to more subtle
FSDG such as:
Programs in the system should not suggest installing nonfree plugins,
documentation, and so on.
https://www.gnu.org/distros/free-system-distribution-guidelines.html
It would be good to point out the precise problems programs in "main" (if
there are indeed problems) and have
https://www.gnu.org/distros/common-distros.html details them.
As far as I remember, "contrib" and "nonfree" are disabled by default. As a
consequence, no "do it yourself" "process of disabling the other
repositories" is required.