I'll admit it at the outset: I'm in a bad mood today.
(Okay, really I can. But in this case, I don't want to).
Read Facebook's terms of service.
The "User Content Posted on the Site" section is particularly relevant here:
When you post User Content to the Site, you authorize and direct us to make such copies thereof as we deem necessary in order to facilitate the posting and storage of the User Content on the Site. By posting User Content to any part of the Site, you automatically grant, and you represent and warrant that you have the right to grant, to the Company an irrevocable, perpetual, non-exclusive, transferable, fully paid, worldwide license (with the right to sublicense) to use, copy, publicly perform, publicly display, reformat, translate, excerpt (in whole or in part) and distribute such User Content for any purpose on or in connection with the Site or the promotion thereof, to prepare derivative works of, or incorporate into other works, such User Content, and to grant and authorize sublicenses of the foregoing.
While IANAL, these seems to render the site completely useless for aspiring writers looking for feedback, as even a private draft shared among friends is licensed to Facebook.
Granted, the traditional LMS is a monolith designed to serve the needs of institutions first, teachers second, and students a very distant third. And yes, a social learning space is a vast improvement. But, a space needs to offer more than just the potential for social learning for it to be a wise choice. Facebook offers some generic functionality that is an improvement over traditional LMS's, but this says more about the sorry state of existing LMS solutions than about the suitability of Facebook as a replacement.
If you want a social learning space, you have a bevy of open source solutions that get the job done more effectively and allow users to retain control of their content and their user data. Moodle, Drupal, or even WPMU are a better place to start.