The tragedy in Romeo and Juliet was a result of many different causes, one of them being their parents themselves. The parents" over protectiveness does not equip their children with the important skill for them to manage or handle their own problems in life. .
For the Montagues, they are always willing to solve Romeo's problems. They would always, "willingly give cure as known", and would always help Romeo to evade them or simply just give him the solutions. This lead to Romeo's inability to solve his own problems that he faced when he was banished. He panicked and could do nothing but shed "womanish tears". Romeo has always been pampered by his parents and never really faced any real problems or their consequences. This is why when having to deal with one, he could not and crumbled.
"Right glad I am that he was not at the fray" claims Lady Montague and had made Romeo soft with her over-emotiveness in her bid to protect Romeo form any form of harm. This is evident when she seems anxious to know if Romeo had been involved in any fighting or the fray. Romeo repeats this later on when he saw that the only way out of his problems was through suicide because he had no other option, and no fighting spirit of his own to go on living.
The Capulets, on the other hand, were protecting Juliet because they did not want any harm to come to her since "the earth hath swallowed all (their) hopes but she". They did not want to lose another daughter, and see her suffer in any way. That was why they chose the way she lived, they felt they "knew best" and by doing that were being too overprotective. Juliet saw this as control over her life and the way she lived. This led to her eventually rebelling and falling in love with Romeo, a Montagues son.
However, the parents are not primarily responsible for the deaths of the two lovers. The lovers had made their own decisions and wrong choices themselves knowingly, which was indeed the eventual cause of the tragedy of the two lovers.
