The purpose which would be best served by a group discussion is the following one:
Considering different points of view.
Since different people see the same issue in a different way, according to their raising, religion, moral beliefs, etc., a group discussion serves the purpose of considering different points of view very well. It is very important to pay close attention to the ways people face a particular topic, since chances are many aspects which had not been considered before can help find, if not a solution, at least a broader and more sensible way to deal with whatever is being discussed.