On Shakespeare's Criticism of Emotion
A general theme seen throughout Shakespeare's play, Romeo and Juliet, is a criticism of people following their emotions. The destruction of many of the characters in the play, and the great loss suffered by all, can be seen as a consequence of the emotional reactions that occur throughout the play.
The two central characters of the play, Romeo and Juliet, are clearly emotional people, as seen in their responses to meeting each other, and even more at the time of their deaths.
There are others, though. Mercutio, when given over to his emotions ends up looking like a fool. Capulet is seen several times reacting emotionally: when Tybalt wants to kill Romeo at the party, and when Juliet says that she will not marry Paris. Tybalt's emotions lead him to rage. Even the whole conflict between the two families probably resulted from them following their emotions.
Within this theme, Shakespeare is demonstrating that following our emotions instead of thinking things out rationally and clearly results in failure, foolishness, or even destruction. This is common for Renaissance writers. Classical Greek culture, where a lot of the Renaissance ideas originated, put a heavy emphasis on this.
In Homer's Iliad, for example, the tragic hero, Achilles', spent most of his time pouting in anger. Partly because he refused to fight, his best friend gets killed. Because he gave in to his emotions, he suffered a great loss. If he had thought things out logically and rationally, he would not have allowed his friend to be in such a place of danger.
Shakespeare presents a similar theme. Capulet's very emotional reaction to Juliet's refusal to marry Paris helped to drive his equally emotional daughter to seek drastic measures to escape her predicament. It was also inconsistent with what he had spoken before to Paris, namely that her consent was necessary for the marriage to take place. If he had thought things out instead of just reacting, he could have postponed the wedding and taken some time to handle the situation rationally. Then he could find out why this change has come about in his daughter instead of sending her to her own destruction.
Juliet's own reactions to the events around her bring about her own destruction. She could have just run away and hid with Romeo, and from there sent a message to her parents that she was married already to Romeo. She could also possibly seek help from the prince, since he might see her marriage as a way to bring peace to the city. There were numerous ways for her to escape destruction, if she would have thought things out clearly and rationally.
Whether Shakespeare intended to include this theme in his play or not, I cannot say; but the theme is there. As a work of literature, the play presents a clear argument in favor of logical, rational thinking.