It’s still ideas the group agrees with. The idea is: that we all disagree with this idea. It’s subtle, until you look at the same story on CNN vs Fox. Two bubbles discussing the same issue with two VERY different emotional valences.
To put it another way: the discussion of these ideas that are oppositional to the community, is not with the intention of seriously considering them. It’s with the intention of dismissing them in a group act of catharsis. It maintains the bubble and safely dispatches an idea that threatened to burst it.