Yes, Macduff does enter the stage with the head of Macbeth. It is clear that Macduff killed him not just because he was a bloody tyrant, but as revenge for Macbeth killing his entire family. However, Macduff was not overly violent and does not seem to have butchered the entire body.
Hail, King! for so thou art. Behold where stands
The usurper's cursed head. The time is free. (Act 5, Scene 7, p. 90)
Macduff is just trying to show that he really did kill Macbeth.
Also, it might have been proof of death. There were so many unnatural things that happened in the play, I could see people questioning whether Macbeth was really dead unless they saw his head on a stake. At the same time, the head continues the violence that pervades the entire play.
Just as Macbeth, the hero, at the beginning of the play "unseams" Macdonwald from the navel to the chops, Macduff had to treat HIS traitor. Macduff is now the hero warrior of Scotland, and it makes sense that he would make such an example of Macbeth since Macduff had such a personal connection.
Macduff fights with and kills Macbeth, hauls the body off stage and reenters a few lines later with the head of Macbeth. Beheading was a common practice in England in the 16th and 17th century. Henry VIII had wives' heads cut off, Elizabeth I had Mary Queen of Scots beheaded. Charles Ist, James Ist son, was beheaded later in the 17th century. In Henry VI, Shakespeare has The Queen carry the head of her dead lover, Suffolk, around with her. Probably there was a "head" kept at the theater for just such purposes (perhaps a cabbage?). Bloody scenes were to be expected in the theater at this time, after all, bear baiting with its blood letting was an alternative form of entertainment.
I am certain that audiences would have felt that Macbeth got what was coming to him and a kind of catharsis was achieved, a fitting parenthesis to the wanton blood letting of Duncan at the outset of the play. The death of a kind and beneficent king atoned for by the death of a king grown into tyrant.
Was not justice served and was it not deserved?
Since this is an opinion question, I can only do that - express my opinion. But for what it's worth, here it is! :)
I think what happened to him - being beheaded - was appropriate for that time period and what happened to traitors when they were executed. The ancient Celts would put the heads of their enemies around their camps as a threat to those who might consider attacking them, and that tradition carried through for many centuries in the British Isles.
For Macduff to enter with Macbeth's head and proclaim Malcolm the rightful king of Scotland just makes sense for the time period and for what Macbeth did to the kingdom of Scotland. It was a show of force and of loyalty to Malcolm that none of these Scottish nobles were ever going to let something like this happen again.
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