TL/DR based on my understanding: You can tell whether a participant in a conversation is serious based on how they respond to criticism. This effectively means a three way handshake: poster, critique, rebuttal. For a serious conversation with serious critics, this means that at least four layers must be present in order to cover both sides: poster, critique, rebuttal, critique rebuttal. The rebuttal shows that the poster is serious; the critique rebuttal shows that the critique is serious. These four layers are referred to as layers 0 through 3.

Unfortunately, in most common web discourse, we typically only see layer 0, and sometimes layer 1. In academic discourse, we often see layer 2, but not layer 3, which usually means that the criticism either isn't serious or isn't very good. Places which do show evidence of all four layers are generally more healthy in terms of conversation.

There's more to it and a lot of good examples, but knowing the above up front may make it easier to frame.

I know this is on the blogroll right now, but since it was originally on Facebook I thought it might be nice to start a place for discussion on LW. Linkposts are also quite a bit more visible than the blogroll.