If the other threads are being responded to or not is irrelevant, as there is no requirement to comment on all threads. The idea of a core group is a label that is assigned to all who frequent the couch thread. The feelings expressed are not due to the couch thread itself but more about how person perceives the thread and chooses to respond to it based on their own insecurities. If one feels like it's an "inside" group that is their issue. The couch is welcoming to all. If you want to jump in, jump in.