OK, Obi-Wan Kenobi says "Only a Sith deals in absolutes," a statement which is an absolute. Hence, Obi-Wan Kenobi is either being highly contradictory or highly hypocritical. Or, the third and most likely option, George Lucas doesn't have a clue how to write dialogue.
This is the exact point that Lucas was making. There are no REAL good or bad guys in the Jedi/Sith war, there are just guys with differing viewpoints on the same thing and are casting each other as the "wrong" ones.