Dolphus, who has suffered from the discrimination of his community, tells the kids to “cry about the simple hell people give other people—without even thinking.” He is saying to the children that are no reasons for the unfairness that Tom Robinson is suffering from. It is simply that people are cruel.
Atticus does not put things so pessimistically, but he does suggest the meaninglessness of the trial. He tells Jem that what had happened has happened before and would happen again. He does not try to justify the decision of the jury, knowing as Dolphus does that there is no justification. He simply puts it into perspective - the actions are not the cause of the moment (or even of man's cruelty), they are the actions of a history of racial prejudice.