In examining the change in "mindscape" in an online class, we were talking about a "civil debate". Setting rules for this in the classroom is a skill we all develop as teachers but in the online realm things are different. There were two pieces that relate to the change in using an online discussion.
First, often what seems acceptable in a F2F encounter can come off cold or abrupt in an online settling. We just don't get the humor or the facial/ body language things that make a contradictory statement not so aggressive.
Second, online discussions can encourage the back of the room reluctant participant because of the feeling of anonymity. Often people are braver about talking online.
Think about it. How does it change your classroom world? How do you change to accommodate the difference?