I don’t agree with the thinking of it.
Facebook is not an alternative, nor built for proper discussions. Subjects become fragmented due to the different ways people interact with Facebook. Also the issue of different levels of personal security sometimes impacting the way a “discussion” can appear.
Facebook is great for some aspects of social interactions on a local level, but can be a clumsy, complicated format at times.
It is also difficult to moderate, easy to manipulate, and just not the right place for certain interactions, especially long running issues.
It all comes down to how you want to interact with your users. Fun and friends chit chat, and a little beyond, fine. But that’s about it. (IMO)
Interesting also that it has been noted that a fair chunk of the content is generated by “the mods”, but surely the core of people who start to create a community do just that to make lay the foundations of what is built on it?