(the loud-shouters, not the smart-thinkers)
A good clue that you are on the express train to Dysfunction Junction is if the emerging group leadership are asking questions based on the concept “do we have to”? As a general rule, in both individual and group assignments, even if you do not “have to”, if you can think of that thing as a possibly relevant thing to do, you almost always should do it, because that could be the thing that makes the difference between a C and a B (if in fact you do have to do it) or between a B and an A (if you don’t have to do it, and you do it, then it gives a good impression of your initiative). It may be true that the majority of the group are not interested in the element being proposed by some of the members. Why not agree that members explore the various angles and elements and bring them back to pool the knowledge? Try to find ways to incorporate multiple perspectives within some kind of a unifying framework. Discouraging group members from adding new layers to the project is a red flag of dysfunction.