Some people say that Tybalt's actions (fighting) are just his trying to defend his family, and stop other people from disrespecting this family.
Q: Would a modern day audience excuse his behaviour in light of this reason, or not? What about an Elizabethan audience? Would they have excused his behaviour at the time?
Audiences, modern and Elizabethan alike, would probably understand the role of Tybalt as foil and assess him as a young, fiery-tempered man who delights in considering himself a defender of the family whether or not a real threat exists. Tybalt's behavior would not be excused by either audience because of their understanding of his nature and the hate-filled motivations behind his actions, as well as his role in the drama.
In Romeo and Juliet, as in other Shakespearean plays, certain characters act as foils, characters whose actions and thoughts contrast with another important character, and by doing so, display more clearly the attributes and flaws of the other. As foils, then, these personages do not have as much character development as the protagonist. As such less analysis and criticism would be given to him. The contrast between Tybalt, who is violent and malicious, and Romeo, who is passionate and more loving, points to the important theme of the destructive nature of violence and hate. For it is only when Romeo allows his love to contain a certain violence that it becomes destructive, and it is his interaction with his foil Tybalt which creates this flaw in Romeo's love.
Further, the contrast between Romeo and Tybalt is best illustrated in Act III, Scene 1 when Tybalt tells Benvolio, "Peace. I hate the word as I hate hell, all Montagues and thee." In contrast, Romeo tells Tybalt that he loves him:
I do protest I never injured thee,
But love thee better than thou canst devise
Till thou shalt know the reason of my love.
And so, good Capulet--which name I tender
As dearly as mine --be satisfied. (3.1.39-43)
As a piece of added knowledge about the opinions of Elizabethan culture on a death like Tybalt's:
Not many people are aware that London, at the time Romeo and Juliet was written, was quite divided regarding a murder that happened due to a feud similar to that of the Montagues and the Capulets. This was a debate on which Shakespeare himself probably would have had an opinion, and it directly relates to Tybalt, his death, and Romeo's exile.
While most people agree Romeo and Juliet was based off the Montecchi and Capuleti feud chronicled in Luigi da Porto, there was a very violent feud that culminated in a death about the time Romeo and Juliet would have been written. The feud was between the Danvers and the Long family. The feud, according to history, was over a destroyed hedge. The two families accused one another of breaking laws and several fights broke out regularly between the servants and the members of the two families.
The death happened in October, 1594. It all started with the death of a servant. In a fight a servant of the Long family killed Danver's servant. Letters passed between the two families. Henry Long was particularly insulting: he wrote in a letter to Charles Danvers that he was going to whip him, calling him "Asse, Puppie, ffoole, and Boye." Charles Danvers was a hothead and so was his brother Henry. Henry had served in the military in France and Norway. It is also very possible that he was considered a gentleman of the first house. All of these make him very similar to Tybalt's character.
On October 4, 1954 the Longs were at dinner when the Danvers broke in and started a fight. In the fight Henry Long stabbed Charles Danvers with a sword (not life-threatening) and Henry Danvers killed Henry Long with a pistol. Both of the Danvers brothers then had to escape into exile in France, while the other fourteen members of the brawl were executed.
During the investigation, the government stopped investigating once they found out it was a "Gentleman's Quarrel" (Wilts Archaeological Society Magazine, vol I). This decision brought about considerable debate in London. The population was split between those who believed that a great injustice had been done in allowing the assassins to flee, and those who thought that the death was connected to the feud and the Danvers brothers were simply part of a fight gone wrong. There were many in London who felt the execution of the fourteen was the injustice. There was a huge outcry at the time throughout England as people demanded to know just what had happened in the fight.
To further connect the incident with the play, Sir John Danvers, the boy's father, died two months after the boys fled to France—similar to Romeo's mother dying of grief in the play. In the end, the boy's mother through another marriage was able to convince Queen Elizabeth to pardon the brothers and they were allowed to return to England in 1598.
Once you know the story, it is easy to argue that Shakespeare was using the current events of the time to add drama to his story. The debate over the death of Henry Long and the Danvers brothers is absolutely reflected in the context of the play. Shakespeare went so far as to actually show the fight on stage. Of course, Mercutio dies rather than suffer a non-fatal wound, perhaps siding with the Danvers' cry of injustice at the exile of the brothers.
This leads to an interesting question: did Shakespeare's play Romeo and Juliet have any influence on Elizabeth's decision to pardon the brothers? Food for thought.