Juliet has a strained relationship with her mother, who loves her but is rather distant. It is the Nurse who has brought Juliet up, having been her wet-nurse and then her Nanny and continues to be employed by the Capulets in this capacity. It is no surprise, then, that Juliet finds the Nurse much more mother-like than her own mother.
Her father is more interested in seeing that she marries well and soon rather than her personal happiness. He tells Paris that although she is "free to choose" her own mate, it must be from a narrow pool that he has approved of, and what's more, he has already selected Paris. He sees no reason why his daughter would object.
In 3.5, Lady Capulet believes Juliet is weeping for Tybault. She is suprised by the reaction and more or less tells her to get over it, she looks stupid. Not exactly a kind response! (Not to mention off-base.)
"Evermore weeping for your cousin's death?
What wilt thou wash him from his grave with tears?
And if thou couldst, thou couldnst not make him live.
Therefore have done: some grief show much of love,
But much of grief shows stills some want of wit." (3.5.70-73)
Her refusal to marry Paris meets with anger, not understanding. She sees no reason why such a match would not "happily make thee a joyful bride," but when Juliet protests, Lady Capulet exasperatedly tells her that she'd better take it up with her father: "Here comes your father now, tell him so yourself / And see how he will take it at your hands" (3.5.124-125).
She doesn't truly side with anyone, but it is clear she is not much on her daughter's side.
Ultimately, no one is completely responsible for another person's actions, but Juliet's parents do contribute to her feelings of desperation. Had they been willing to put aside their own grudges and pride long enough to listen to Juliet's pleading for a delay in the marriage to County Paris or even care that Juliet does not want to marry him, things would have surely ended differently. But they are not alone in culpability for their daughter's death. Romeo's impetuous nature plays a part as does the Friar's imperfect planning. Moreover, Fate itself seems to be involved. (Consider the timing of the quarantine that prohibits Friar John from delivering a timely message to Romeo and the subsequent misinformation he receives. Consider the timing of Romeo's suicide just moments before Juliet awakens. These events and more seem to indicate (as does the prologue) that fate is against the young lovers.) But, as I said in the beginning, Juliet is ultimately responsible for her own death. It is she who chooses suicide.
I think Juliet is ultimately responsible for her death; however, myriad adults in her life have been negligent in their care of her.
The most obvious, perhaps, is her parents' continuation of the feud. The resulting situation makes Juliet believe that she cannot speak with her parents about Romeo and it forces their connection to be illicit even before it begins.
The nurse is also negligent in her care for Juliet. Although she warns Romeo that it would be unkind of him to mistreat Juliet, she very quickly glosses over her objections and is more than willing to be an accomplice in bringing the ladder to Juliet's window. She seems more concerned with whether or not Romeo's "man" can be trusted to keep a secret than with Juliet's well-being. (Add to this the fact that she went along with the plan even though she is convinced that Juliet has made a poor choice--she says Romeo is attractive, granted, but Juliet does not know how to choose a man).
Finally, the Friar...he is a man of the cloth and should offer careful advice--which he does, if one listens; however, like the nurse, he voices his concern yet acts in the opposite way.
They are all, to some extent, culpable; yet, still, Juliet is the one who ultimately makes the decision and the blame must rest with her.
Juliet's parents were acting within the guidelines for parents of the time-period. A loving father would have arranged a marriage for his daughter. Her mother would not have been expected to have extensive contact with her child due to her duties as lady of the household. A nurse would have taken over, as did the Nurse for Juliet. The society in which the characters lived would have molded the actions of all involved. Juliet stepped outside her role as an obedient child when she did not accept her marriage to Paris. The audience in Shakespeare's time would have expected her to be punished for this action. Romeo also did not go about things the correct way. The audience would have felt Paris more deserving of Juliet because he was "jumping through the hoops" to wed Juliet.The feud was more or less ignored, not really penalized by their laws, the Prince acted only when it became an inconvience for the city.This encouraged a complacent acceptance of the feud. All characters involved were victims of their society's code of expected behaviors. On a larger scope, the characters within the play were all victims of the themes of Shakespeare's work: The innocent pay the price for the sins of the fathers; going against accepted traditions creates havoc and grief; and impulsive action brings about regrettable results.
It is more of the society that this play takes place which is responsible for the death of Juliet. This being the Patriarchal society in which men have authority over their woman.
If they didn't live in this society then Juliet would have freely been able to choose the man she marries and not have to pretend to fake her death in order to be with the man she loves.