I think discussions within a large group does not really work. Following are the reasons I can think of:
1. Bigger the group, diverse their experience and expectations. It‘s very difficult to satisfy every one.
2. With bigger groups, it‘s difficult for people to open up fast and hence the atmosphere becomes more formal.
3. It takes time to relate to people and communicate with them effectively
4. Since it‘s a bigger group, the distance between people increases. This makes it difficult to see and hear the person clearly. We also miss-out on the body language.
5. With a bigger group, it‘s difficult to make eye contact and some people tend to drift away.
As a result of the above points
1. The discussion tends to get one sided or the group divides into subgroups.
2. It gets difficult for every one to contribute equally to the discussion and take it in a particular direction.
3. Focus of the topic under discussion gets lost very quickly