One of the toughest things to control for effective communication is getting people in a group to listen to each other.  People love to talk about their ideas if: 1) it's a safe environment; 2) other people are truly interested, and 3) they're not going to be disrespected.  Facilitators 1) direct the traffic (asking specific people to contribute while politely having others wait their turn), 2) keep things focused on the compelling topic at hand, and 3) help set mutually-approved "ground rules" that disallows people interrupting other people.

Without trained facilitators, it's a mutually-destructive chaos that often ends in hurt feelings, anger, and fighting rather than productive discussion.

Dan