What is the theme of "Romeo and Juliet?"What is the main moral of the story?

In the play 'Romeo and Juliet' by William Shakespeare, on of the most prominent themes is suggested by the quote 'a plague on both your houses.' The moral relating to this is that it is wrong, dangerous,pointless and counter-productive to bear grudges - particularly ones that ocurred so far back in time as to be history themselves, the original reason forgotten about. yet, the damge they do casts its shadow forward in time to influence wars, hatred,atrocities and even the emotional well-being of descendants hundreds of years later (such as the innocent children Romeo and Juliet.) Riots and public disorder have wreaked havoc in the towns of the Montagues and the Capulets as rival factions squabble and disturb the peace. The Prince is angry, and blames both,almost bringing down a curse on the families if they don't stop - Romeo and Juliet are lost to their families and die becuase of the pointless hatred between them.