Dolphus allows people to think of him as a drunk and a miscreant to draw attention from the fact that his real "crime" as they might see it, is his relationship with a black woman.

This allows townspeople to excuse his black mistress, and they chalk it up to his drinking.

Dolphus Raymond is probably the most progressive citizen of Maycomb when it comes to race issues.  He comes from a wealthy family in Maycomb but lives with his black mistress and mixed children.  This would have been considered scandalous in this small southern community.  Raymond, however, detests the racist privilege of the white citizens and chooses to live his life free from the sentiments of the other townspeople.  However, he has a secret.  In order to make it easier for people to accept this behavior, he pretends to be an alcoholic.  He drinks something out of a paper bag; we learn that it's just Coca-Cola, but he puts on this charade to be more accepted by Maycomb's society.  It's sad to think that it is better to be considered an alcoholic than someone who lives with and accepts blacks, but that is the way it is in Maycomb.  On the other hand, it is also sad that Raymond cannot stand up to the people of Maycomb and openly live his principles.   Raymond is a symbol of a changing Maycomb, and therefore, the changing values of the South.  He is the future in race relations, and luckily, gives Scout and Jem a view of his values and beliefs when they realize that he is not a drunk but someone who is accepting of other races.