How does dill react to this part of the trial? why is this, in your opinion?

In Dill's reaction to the trial which if found in the book of To Kill A Mockingbird, he seems mad and upset because of how he sees how Tom is being treated so poorly. He had said a statement where he seems to be mad of how Tom is being treated. The reason why Dill is reacting this way was because unlike with the people he's with, he doesn't have any experience of watching trials like this happen for he has never gone to one until now, so he was mad for seeing the trial for himself.