In my opinion, Shakespeare is warning his audiences about the folly of impulsive behavior and infatuation vs. real love.  Neither Romeo nor Juliet think about their actions before they do them.  They merely react to situations and go with their initial impulses.  Neither thinks ahead to look for alternative solutions to the problem of their families' possible reactions to their love affair.  Mr. Capulet was already beginning to soften his thoughts regarding the feud after speaking with the Prince, and when he was told that Romeo had crashed the Capulet party, Mr. Capulet actually commented that he'd heard good things about young Romeo.  Had Romeo and Juliet come to him, he might have relented after the initial shock.  Infatuation, not true love, led them to rush into marriage.   Whenever a problem arose, the immediate reaction was "I want to die!"... check out just how many times both Romeo and Juliet indicate this thought.  Shakespeare's message seems to warn young lovers against impulsive behavior and to look for viable solutions to problems.  Also, had the lovers come forward with the truth, many lives would not have been lost: Mercutio, Tybalt, Paris, as well as the two lovers.