Typically, I feel that steering people back towards the matter of discussion is best--however, sometimes a conversation evolves and envelops a greater amount of content outside the scope of the original topic. However, when a thread becomes a shouting match or is filled with bickering--and warnings and pointings do not derail those discussions, then the thread should be closed.
One of my threads was closed recently. Originally I was quite upset by this. I quickly changed my mind after I had seen what things had deteriorated into. The mods would have been remiss had they not done so--despite my feelings on the subject.