“I think it is only natural progression for a topic to include surrounding issues.”
I agree. Discussions often include propositions taking the form of a logical argument. Discussions might also include participants exploring various ideas either underpinning or refuting a certain perspective, or both. This necessitates a measure of digression from the main subject to sub-subjects.
When the discussion is of logical arguments this can become more tedious because arguments have to be logical in form in order to be sound; hence examining the form of argument becomes a substantive point of discussion. Those who do not understand the mechanics of this could easily misunderstand this as off-topic when in fact it’s precisely on-topic.
Once an argument is shown (or acceded) to be logical in form then each of its premises require proving in order for the argument's logical conclusion to be sound. Premises used within a logical argument can direct evidence (e.g., an observed fact) or they could be conclusions of logical arguments. If a premise used in one argument is the conclusion of a previous logical argument then that previous logical argument becomes an integral part of the current discussion. The depths of this discussion could become enormous. Again, this is something that could easily be misread as off-topic when in fact it’s precisely on-topic.
Hence saying a discussion naturally has a progression that includes surrounding issues is true, and I’d say is often an understatement.
“I suppose once a thread degenerates into a slagging match with no sign of any topic at all...it is a clear indication the comments are 'off topic' and just poking each other with sticks.”
The most telling aspect of someone who’s not participating in good-faith is when he or she fails to answer questions asked for precisely what those questions ask. When this starts to occur, in my experience the participant either holds a strong unrelenting personal bias that recognizes no reason or else they fear being refuted. I don’t understand either of these. We should all want to learn what is or is not sound, even if it means we happen to be wrong about something. Being wrong is something we all experience and there’s no shame in it.
In my mind it’s the lack of good faith participation that is the ultimate degeneration of a discussion.
PS for cha ching: No, I am not an English teacher.