I could probably come up with at least half dozen notable groups around ENWorld that I would casually refer to as "cliques". Cliques aren't necessary exclusive in the sense that you need a membership card to get it. It can just be a scenario where a few main people get most of the attention. That is absolutely the case here; there are certain topics that will attract groups of people that can dominate the discussion. It's not that they're specifically excluding new people, but rather that a few people can post so much that outside opinions get lost. Sometimes it's intentional, sometimes it's not. Even in purely social threads like the Hive it can be hard for a poster who's completely new to the site to jump in and join a conversation with people who have known each other for years, even if the group does their best to be accepting. Honestly, cliques are kind of inevitable for a forum this large and old.
One thing that I do find interesting is that some of what I would call cliques here aren't necessarily friends. There's a couple of topics that tend to pull in the same groups of people that are very adversarial with each other, to the point of excluding outside voices from the discussion.
