Good Fences Make Good Neighbours - A Lesson in Boundaries

They say that good fences make good neighbours.

I remember reading this line in a Robert Frost poem in university, and I always found it a little disconcerting.

Really?  Good fences make good neighbours?

I, in my Utopian brain, thought it pretty primitive.  We should all live as one, no?  The planet belongs to all of us… who are we to divide it up into little grass squares with symbolic partitions in between?

Can’t we all just… get along???