Creating a set of discussion guidelines with your students is a good way to teach skills and gain "buy in" on how to conduct dialogues as a community of learners. One way to do this is to put students into small groups at the beginning of the term and let them spend 7-10 minutes coming up with discussion guidelines for the class. Then come together as a group, discuss the ideas and come to consensus. Talk about how you think dominators or people who never contribute should be handled. Ask what the class should do if a topic sparks a lot of emotion or feelings of hostility. Thinking through these issues beforehand can help students find constructive ways to manage a large group discussion.
If a discussion topic has the potential for generating a lot of emotions or going off track, review your discussion guidelines before the discussion begins.