What are some quotes you could use to argue Romeo and Juliet are to blame for their own deaths?

After Tybalt slays Romeo's friend, Mercutio, Romeo becomes enraged, saying,

My reputation [is] stained

With Tybalt's slander [...]

O sweet Juliet,

Thy beauty hath made me effeminate

And in my temper softened valor's steel (III.1.116-120).  

Romeo blames Juliet's love for making him weak and soft, like a woman. Rather than exercise forethought or try to remain calm as he did previously, Romeo acts impulsively, killing Tybalt, a crime for which he knows the punishment is death. He is lucky to be banished instead.

Juliet is likewise willing to die if she cannot work out a way to be with Romeo after he is exiled and her parents promise the County Paris he can marry her. When the Friar wonders if "[She has] the strength of will to slay [her]self" and drink a potion that will make her seem as one dead, she exclaims she would rather leap from a tower or be confined with serpents or bears than marry Paris (IV.1.73). Like Romeo, Juliet is willing to take her own life. Although Juliet worries she might never wake up before she drinks the potion, she drinks it anyway.  

Friar Lawrence even attempts to warn Romeo about his own and Juliet's impulsive natures, saying, "These violent delights have violent ends / And in their triumph die, like fire and powder, / Which, as they kiss, consume" (II.6.9-11). Therefore, he advises them to "love moderately" (II.6.14). Of course, Romeo and Juliet do not take the Friar's advice. Everything they do is immoderate; they are intense and impulsive in the extreme. In this way, one might blame them for their own deaths.