A theory I subscribe to personally is:
A collective mind, though more powerful, ultimately only comes up with one idea, and the perspective offered is all internal. Whereas, an intelligence that comes from multitudes of sources, comes up with many ideas and external perspectives that compete or compliment one another, in theory providing a much more productive answer.
Obviously, this connects only loosely to the debate of full public vs. partial private/public, but I think it has some pretty decent correlation.
Human personalities run a full gamut of the spectrum, and that creates a sort of balance. If you create a situation wherein introverts are denied their prime operation, you're essentially crippling the balance. We've all seen what happens when a mostly E society tries to transform an I into an E, and it's not usually pretty...