What textual evidence helps prove that Mercutio is responsible for the deaths of Romeo and Juliet?

Upon Mercutio’s death, he claims that the “plague” on the Capulet and Montague households is why he is dying. However, when taking a closer look at Act III, Scene I, it becomes clear that not only his death, but also the deaths of Romeo and Juliet could have been avoided had he kept his cool.

At the beginning of Act III, Scene I, Benvolio and Mercutio are strolling around in a public place when they run into Tybalt, who is looking for Romeo. Mercutio attempts to provoke Tybalt, which doesn’t work, especially when Romeo enters the scene. Romeo refuses to fight Tybalt, and Mercutio is disgusted by Romeo’s behavior, so he draws his own sword:

O calm, dishonourable, vile submission!

Alla stoccata carries it away.

[Draws]

Tybalt, you rat-catcher, will you walk?

Romeo begs him to put his sword away, but he refuses. Tybalt and Mercutio fight, and Mercutio is eventually fatally injured. He blames his death on the dispute between the Capulets and the Montagues: “A plague o’ both your houses!”

Once Mercutio dies, Romeo is furious. He recognizes that Tybalt is technically his cousin now, but he can’t hold in his anger since Mercutio was a dear friend:

Now, Tybalt, take the villain back again,

That late thou gavest me; for Mercutio’s soul

Is but a little way above our heads,

Staying for thine to keep him company:

Either thou, or I, or both, must go with him.

Their fight concludes with Romeo killing Tybalt.

This shows that Mercutio could be held responsible for the deaths of Romeo and Juliet because Tybalt wasn’t even interested in fighting Mercutio, but because Romeo didn’t want to fight Tybalt, he pursued fighting Tybalt, causing his own death. Mercutio’s death brought a maddening fury to Romeo, causing him to fight Tybalt, which led to Tybalt’s death. The Prince then banished Romeo from Verona, which led the Friar to create a dramatic plan in order to ensure that Romeo and Juliet could be together. When the plan didn’t work out, Romeo was under the belief that Juliet was dead, which gave him no reason to live anymore; thus, Romeo killed himself in Juliet’s tomb. Once Juliet awoke to find Romeo dead, she, too, killed herself.