This is an excellent question. As we look at the book, we can say that there is really no one who defends Atticus. He is so much in the minority in his opinions that most people don't even see eye to eye with him. This does not mean that others do not share his convictions. Ms. Maudie certainly does, as do people like Heck Tate. But they do not protect or defend him. We can see this when Atticus is almost beaten by a mob. No one is there except for Scout. In fact, if Scout hadn't been there, Atticus would have gotten hurt.
The people are saying that Atticus should not defend a black man. They are so racist that they are blind, and we can say that they do not care about justice. For the town it is a black and white issue.
Atticus knows this, but he still holds firmly to his convictions. In fact, he knows that he is going to lose the trial, but he will still try his best to win. Here is a small dialogue between Atticus and Scout:
“Atticus, are we going to win it?” “No, honey.” “Then why—” “Simply because we were licked a hundred years before we started is no reason for us not to try to win,” Atticus said.
In the book, Atticus is defending a black man named Tom Robinson. He is accused of raping a white woman named Mayella. Although it at first seems like Atticus is doing this because of his beliefs (he says that he wouldn't be able to look at his children if he didn't do this), but late you find out that he was appointed by the judge.
The town of Macomb is extremely racist. If you think back to poor Tim Johnson, the dog represents the racism of Maycomb as a sickness. Remember that the dog was the Tow's dog and was very sickly. After Atticus, who is going against racism by defending a black man, shoots Tim, the book says he dies in a heap of brown and white. When Tom goes to court, all anyone cares about is that he's a black man and so they assumed es is guilty. Peope also often all Atticus a 'Nigger Lover' as an insult to Scout.
Atticus knows that Maycomb is very racits but still defends his beliefs by defending Tom. Atticus is not easily swayed by what others think of him. Atticus know he is going to loose because of racism, but this is about self respect to him. He is trying to be better than racism. Atticus simoly ignores gossip and keeps his head held high.