Fear.  It is at times the emotion that grips us when we consider another Christian group, be the group Roman Catholic or Eastern Orthodox or Protestant.  In intercultural communication terms, this is called "intergroup anxiety": we are anxious that contact with another Christian religious group will threaten our personal, spiritual, and theological well-being.  At the same time, we can wrongly idealize another group, looking at that group through rose-colored glasses.  That is just as much a no-no as inter-Christian anxiety.