SPRINGFIELD — Ethical rules for lawyers say they should not let the interests of one client affect their representation of another.But public defenders are required by law to take on certain defendants, and some could have adverse interests when, say, they blame each other for the crime.Those duties clashed in arguments this week at the state’s highest court after Cook County Public Defender Amy P. Campanelli was deemed in contempt by a Cook County judge for refusing to represent a murder defendant after taking …