How does Rose use Juror 10 as an example of bigotry?

In the play, Juror Ten is violently prejudiced against anyone who comes from a slum. "You can't believe a word they say," he says early in act 1. Note that he does not say "he," meaning the defendant, but "they," the group as a whole, which shows that he cannot make a fair judgment about individual guilt. Juror Nine, the old man with much experience of life, sees this immediately and rebukes Juror Ten ("Since when is dishonesty a group characteristic?"). But Juror Ten's bigotry continues to smolder before finally erupting in a long speech near the end that leads the other jurors to reject him. The message is clear that such irrational prejudice is incompatible with justice. Juror Four also shows signs of such prejudice, though he couches it in more acceptable words: "The children who come out of slum backgrounds are potential menaces to society."