The one element that West Side Story has that saves the evening from unmitigated tragedy-an element that Shakespeare's Romeo and Juliet does not have-is its sense of forgiveness. Tony, maturing and trying to escape the cycle of violence, dies while trying to stop his peers from their self-imposed code of honor. When, in their immaturity, the Jets and the Sharks allow their emotions to escalate the violence, it is their own who are hurt, and only then do the gangs begin to understand what all their posturing, taunting and insecurities have wrought. The show may make fun of Officer Krupke and all the bleeding hearts that try to excuse the actions of delinquents on sociological grounds, but the show itself, while in no way condoning the actions or shying away from their consequences, still has a moment of togetherness and hope at the end.
It's that hope that makes the intensity of the evening bearable, and makes West Side Story eternal.