In Romeo & Juliet, why do you think Mercutio continues saying, “A plague on both your houses!”? What does it mean, and why does he say it?

This happens to be one of the most significant quotes throughout the whole play!! I LOVE it!! Okay, so basically, when Mercutio says this, he's cursing the Capulet family AND the Montague family. He said this right after he was stabbed by Tybalt; Mercutio knew that he was going to die, and he was VERY angry. The main thing from this quote involves fate (believe it or not). If Romeo would have never went to the Capulet party, he would've never met Juliet, and the two of them would've never fallen in love. If this wouldn't have happened, then the fight between Mercutio and Tybalt could have been prevented. If this were the case, then Mercutio would have never been killed. All in all, Mercutio is saying that both sides are at fault. He's not blaming it just on Tybalt or the Capulet family, but instead blaming it on Romeo, Juliet, the feud between the families, etc.