[LeonB]

If you’re a lawyer representing a mass murderer you must still represent the interests of the client. To not do so would see you disbarred.

So professional ethics can run counter to what a polite member of society would normally wish to do.

[7402]

Although I believe lawyers are still required to disclose to the authorities any information concerning their clients' intention to commit a crime in the future - so the obligation to represent a client's interests is not unlimited.