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.