Do you think Shakespeare’s portrayal of the commoners in Act 1 of Julius Caesar is realistic?

Shakespeare’s portrayal of the commoners represents a way some people think, which is to be easily persuaded.  Not only commoners, but educated people might also be easily persuaded to change their mind from one position to the next. Indeed, the “mob mentality” we see in the commoner’s new alligeance to Caesar is similar to the ease with which Cassius convinces Brutus, with no real evidence, that Caesar aspires to be crowned and should therefore be murdered.  The attitude of Marullus and Flavius to the commoners in this scene is very rude: these men are only going about their business, and they want to see “Caesar and to rejoice in his triumph” (1.1 35), which hardly compares to their own evil intentions of murder. So, to answer you question more directly, I think Shakespeare’s portrayal of the commoners serves a dramatic purpose of introducing a theme of how people can be persuaded and of characterizing Caesar’s enemies more than it serves the purpose of realistically portraying an entire group of people. It is a way of thought, not a class of people, that interests Shakespeare here.