In writing in public, students are forced to confront ideas and positions that contradict their own as others comment on, challenge, and respond to their work. They develop technological skills by using platforms and tools they might not have otherwise engaged in. These capacities are as important as their ability to write, as they also encourage students to listen and think; the act of communicating is not merely about speaking.
So much more than in the LMS or other controlled spaces. Let them be real and deal with it! It's the future.