Ben Kuhn wrote a post in which he looks at problems with the Effective Altruism movement. One of his observations is that the quality of discussion in the Facebook group is getting worse:

The discourse around effective altruism in e.g. the Facebook group used to be of fairly high quality. But as the movement grows, the traditional venues of discussion are getting inundated with new people who haven't absorbed the norms of discussion or standards of proof yet. If this is not rectified quickly, the EA community will cease to be useful at all: there will be no venue in which a group truth-seeking process can operate.

While I agree that it's valuable to have places with good discussion, I'm not sure the group really is going downhill. People's view of history is notoriously bad, but unlike in-person communities with an online one all the data is saved. Facebook's interface to history involves huge amounts of "infinite" scrolling, however, so it's hard to get at that history. So for people interested in looking over the posts to the group I've extracted an ugly list.

The group has been around for a year and has had 860 posts. I don't see any clear trend in usefulness or insight.

(One flaw is that this won't include posts that were removed by the mods as duplicates, irrelevant, etc. Those posts are still seen by a lot of people, though, and still act to bring down the quality of discussion.)