So, an operating system can born "free" (free as in speech, in the GNU sense)

    and then, become "non-free" just because some users decided to create a way

    to ease installations of software that "just can't be shipped with the system"?
You've formulated a very broad description, which applies to the act

of putting a non-free program in the ports system, and equally to many

other acts whose nature is different.  For instance, the program might

or might not be free; the easier way might or might not be included in

OpenBSD.  I might say the act was bad, or I might say it was good,

depending on the details not specified.
If "some users" write a way to "ease installation" of some non-free

program, and distribution D doesn't include this way in its

distribution or publicize it, then those users have done something bad

but distribution D is not responsible for what they did.
However, if distribution D includes this "easier way to install" in

its ports system, by doing so distribution D endorses it and takes on

the ethical responsibility for it.
I say "distribution D" because this is the same for any distribution,

whether it's a distribution of the BSD system, or a distribution the

GNU/Linux system, or whatever.