Privileged Communication in the US Legal System

I am asking this is responce to the release of the September-October Lincoln/Douglas debate resolution, “Resolved: In the US judicial system, truth seeking ought to take precedence over privileged communication.” Now, I understand what privileged communication is (communication between Attorney and Client, Doctor/Patient, Wife/Husband, Priest/Penitent). What I do not understand is why it is so important. To any legal experts out there: Why is keeping these statements out of court important? What would be the ramifications of making these statements admissable? And finally, are there any law professors, lawyers or judges that have written at length about this, and would be good points for research? Any help would be appreciated.