One question particularly relevant for this list is why I don't recommend OpenBSD. It is not about what the system allows. (Any
general purpose system allows doing anything at all.) It is about
what the system suggests to the user.
Since I consider non-free software to be unethical and antisocial, I
think it would be wrong for me to recommend it to others. Therefore, if a collection of software contains (or suggests installation of) some non-free program, I do not recommend it. The systems I recommend are therefore those that do not contain (or suggest installation of) non-free software.
From what I have heard, OpenBSD does not contain non-free software (though I am not sure whether it contains any non-free firmware
blobs). However, its ports system does suggest non-free programs, or at least so I was told when I looked for some BSD variant that I could recommend. I therefore exercise my freedom of speech by not including OpenBSD in the list of systems that I recommend to the public.
I could recommend OpenBSD privately with a clear conscience to someone I know will not install those non-free programs, but it is rare that I am asked for such recommendations, and I know of no practical reason to prefer OpenBSD to gNewSense.