Someone whose main function in a group discussion is to contribute and debate ideas is called a ?

Someone whose main function in a group discussion is to contribute and debate ideas is called a gate keeper.

two essential roles in group discussion are gate  keeping and time keeping.

gate  keeping is a form  of verbal traffic management. a gate keeper  attempts to spread participation by encouraging those who have not recently spoken to share their thoughts and questions.

gate  keeping is also necessary when several people wish to speak at once. at such times, encouraging the less assertive members to continue first will often facilitate communication. gate  keeping also the group move efficiently from one topic to the next and through the steps of the discussion outline.

The answer is "he was bad enough in all conscience, but the devil himself could not temp him to turn slave-trader. satirical is a synonym for sarcastic. so when the author says that tom walker could not be tempted by the devil he does not literally mean "the devil" but he means that he is too morally upright to become a slave-trader.