What are denominations all about?

I have heard it said many times by pre-Christians, or by disheartened former 'Followers of the Way"... "You all call yourselves Christians, BUT... you don't seem to even like each other, or worse... seem to hate each other. Why would I want to join up with you?"And, indeed... why would anyone want to join a disfunctional 'family'? What part of Jesus' prayer recorded in the Gospel of John, chapter 17 do we not understand? What part of "becoming one" did we miss? So, we have tens of thousands of different denominations and sects and independent groups ALL claiming to be true followers of the Christ who prayed for unity... often living openly in competetive disregard for each other. What is wrong with this picture? Is there actually anything wrong with thinking differently than another Christian group? What can we DO to change this perception (or reality) of disunity? Should we try to become one super denomination? Whose ideas would we use as the "right" ones? Help me here....!