"Here's much to do with hate, but more with love," Romeo says at the play's beginning, and the dynamics of extreme emotion define the tone of the play (1.1.7). Romeo and Juliet deals in extremes that overlap or transform into each other. The Friar's lone voice of moderation is drowned out by storms of passion and violence; the insults tossed back and forth between the Montagues and Capulets alternate with Romeo and Juliet's loving exchanges of vows.
Even the play's highly sexualized language is often discussed in violent terms: "If he be married, / my grave is like to be my wedding bed," Juliet says before she learns Romeo's identity (1.5.9), and then, "I should kill thee with much cherishing" (2.2.27). All this strong emotion demands resolution—and it doesn't seem to much matter whether we get that resolution through kiss or through a sword.