IM and SMS aren't public forums where people you don't know can barge in with their own take on what you just wrote, though. IRC can be, but it would be very difficult to have a grasp on every IRC conversation happening everywhere so you could respond to something you find incredulous.

Unlike Twitter, which incentivizes people carrying on infinite numbers of asynchronous conversations, and encourages people to find them by bringing up 'interesting' ones on the timeline.