In Act One scene Two Lord Capulet indicates that he will only agree to arrange a marriage between Juliet and Paris (or any other suitor, for that matter) if Juliet believes it to be true love. He urges Paris to wait two years so that is old enough to make such a weighty decision. However, when Juliet later resists the arranged marriage to Paris, Capulet is fit to be tied, and it becomes apparent that he thought Juliet would acquiesce to his wishes for her. He threatens to throw her out in the street to die. Moreover, he doesn't even know the true intent for Juliet's feelings; he assumes that she grieves for Tybalt when in fact she grieves over Romeo's banishment. Capulet does not listen to Juliet nor does he care to; he is more concerned that the public might think poorly of him for having a wedding so soon after Tybalt's death. He was a true PR man.
The Montagues, on the other hand, are closer to Romeo than the Capulets are to Juliet. However, Shakespeare does not invest much time in developing their relationship. Still, the difference between the parents is clear in Act Five when Montague grieves his son's death and reports that Lady Montague has died from her grieving.
"Now, by Saint Peter's Church and Peter too,
He shall not make me there a joyful bride.
I wonder at this haste; that I must wed
Ere he, that should be husband, comes to woo.
I pray you, tell my lord and father, madam,
I will not marry yet; and, when I do, I swear,
It shall be Romeo, whom you know I hate,
Rather than Paris..."
Lady Capulet only hears that her daughter will not marry Paris. Capulet does the same thing a few lines later when he only hears his daughter's disobedience. He makes no attempt to truly understand what she says.
Good father, I beseech you on my knees,
Hear me with patience but to speak a word.
Hang thee, young baggage! disobedient wretch!
I tell thee what: get thee to church o' Thursday,
Or never after look me in the face:
Speak not, reply not, do not answer me;
Even after his daughter's plea Capulet refuses to see his daughter as anything but a "disobedient wretch."
When faced with such deaf ears, Juliet feels she has no other choice but to leave her parents.