His fault is forgiven in order to prevent further bloodshed and to promote peace and reconciliation between the two families. The law should end Tybalt's life to bring justice for his actions and to deter future acts of violence.
Montague, who acts as Romeo's advocate at the trial, argues that Tybalt had already broken the law and incurred the death penalty by killing Mercutio. Romeo was therefore only carrying out the law by punishing Tybalt. "His fault concludes but what the law should end, the life of Tybalt." The Prince has no desire to encourage vigilante justice, so he does not acquit Romeo on this plea, but only reduces his sentence from death to banishment
My client Romeo stands accused of the death of Tybalt. I will endeavour to prove to you that he killed Tybalt purely as a matter of self defence. Tybalt was a known troublemaker with a short temper and had long harboured a grudge against Romeo. On the day in question he was looking for a fight and picked one with Romeo's cousin Mercutio which resulted in the death of Mercutio, a totally innocent man, at the hand of this Tybalt. Tybalt then picked a fight with my client Romeo who was forced to defend his life, if not his honour. Unfortunately Tybalt was killed. The fault lay with that ugly brute Tybalt not with my dishy young client Romeo.
Tybalt.
By fighting with Mercutio, Tybalt incurred the death sentence according to the edict promulgated by the Prince in Act 1 Scene 1 which made fighting in the streets a capital offence. Montague argues that Tybalt's life was forfeit anyway and that Romeo was just carrying out the sentence of the law.
The prince doesn't sentence Romeo to death because: 1) If Romeo didn't kill Tybalt, he would've been executed anyway 2) Tybalt would've killed Romeo if Mercutio hadn't stepped in. Mercutio died because Tybalt killed him, and Tybalt died because Romeo killed him. 3) Tybalt paid the price for killing Mercutio, and when the prince asked who would "pay" for Mercutio's death, Montague said Romeo shouldn't have to because they were good friends, and Romeo killed Tybalt to avenge Mercutio.
Because the guy he killed had already committed a capital offence by killing Mercutio. The Montagues argue that Romeo shouldn't be punished for doing to Tybalt what the hangman was going to do anyway. The prince takes this into consideration, but only reduces Romeo's sentence, as he still shouldn't be taking the law into his own hands.
All research today in the year of 2012 concludes to chocolate.
Nothing, really. Romeo reacts to Tybalt's actions on his own volition. Because he doesn't want to see his cousin and his friend fighting he tries to break up the fight. Because Tybalt killed Mercutio, Romeo wanted revenge on Tybalt. But Tybalt didn't make Romeo seek revenge; Romeo could have walked away from it all, and watched Tybalt be executed for his crime while he gets to spend the rest of his life with Juliet.
Tybalt sent Romeo a letter challenging him to a duel.
At the end of Act III Scene 1 of Romeo and Juliet, the Prince, who represents the law, holds a trial to determine what to do about the killing of Tybalt. Back in Act I he made a decree that people fighting in the streets would be put to death. Mrs. Capulet, Tybalt's auntie, takes the part of prosecutor. Montague, Romeo's dad, takes the part of defence counsel. Benvolio is the chief witness, and gives his evidence truthfully as we know because we are also witnesses to what happened.Mrs. Capulet, for the prosecution, says that Benvolio is not an impartial witness, and even so he admits that it was Romeo who killed Tybalt. Probably, she says, a bunch of Montagues jumped poor defenceless Tybalt. She concludes with the ringing "Romeo slew Tybalt; Romeo must not live."The Prince is, however, prepared to accept Benvolio's account. How, he asks, should we deal with the fact that Tybalt had only minutes before killed Mercutio in a different street brawl. Defense Counsel Montague hears his cue and speaks up. By killing Mercutio in a street brawl, Tybalt broke the same law that is being urged against Romeo, he says, so Tybalt's life was forfeit in any case. Romeo was just doing what the Prince's hangman would have been required to do eventually. However he also mentions that Romeo was Mercutio's friend. This is probably a bad move strategically, since it suggests that Romeo's motive was not enforcing the law but revenge for the death of his friend (as is in fact the case). This "getting revenge for my friend" thing is what keeps fuelling the feud. The Prince cannot pardon Romeo completely under these circumstances; he can only commute the sentence.
Tybalt challenges Romeo to a sword fight, which Romeo declines, but Mercutio accepts in Romeo's place. Tybalt wounds Mercutio when Romeo attempts to break up their fight. Mercutio dies and, in a rage, Romeo kills Tybalt. This results in the Prince banishing Romeo for life, only hours after his secret marriage to Juliet.
Mercutio does not "save Romeo" in the play by fighting Tybalt. Tybalt is about to walk away in contempt of the coward Romeo who will not fight him, and Mercutio gets involved, ostensibly to save Romeo's honour but basically just to get into a scrap. In the 1996 Baz Luhrman movie, the director has Tybalt beating Romeo when he will not fight, which does prompt Mercutio to join the fight. In that version Mercutio thinks that Tybalt will kill Romeo and that he needs to intervene to save his life. It's a more flattering read for Mercutio than what Shakespeare wrote.