Mailing-lists have a problem: They give everyone, and every post, a similar voice. As individuals, we can killfile consistently annoying posters, but that doesn't scale very well, and it gives false positives as well as false negatives. (consistently annoying people sometimes post good stuff - usually constructive people sometimes post annoying stuff)
Allowing people to moderate, and allowing (but not enforcing) people to give more visibility to higher moderated posts, help the signal-noise ratio a lot. If there's enough contributors, that is needed because reading it all is simply impractical, or even impossible.