Some people, when confronted with what West Side Story is really about, don't want to hear about it. 

They prefer to think of WSS as a tragic romance, about two star crossed lovers, just like in Romeo and Juliette, but with great dancing and better songs.  They ignore that WSS is musical theater "inspired" by R&J, not based on it.  WSS is powered by the racial conflict between the Sharks and Jets, and that conflict is racial.  To not put the antagonism, and real danger between the Sharks and Jets front and center in WSS is to do the show a disservice and dilute it's important message. 

As Brooks Atkinson said in his review of the original production, "Gang warfare is the material of "West Side Story," and very little of the hideousness has been left out."

Especially now, in our times of increased racial tension, WSS asks audiences to make a decision about where they stand.  Sadly, some audience members do not come to musicals to be reminded of unpleasent things.  And in choosing not to see, they make a choice that all too many people make.