"If this is the case, should the authors of threads continually attempt to keep the argument where they intended it? Should the person who opens the discussion be the sheriff of that discussion?"
Lloyd:
If they don't like the tangents perhaps they should but I don't think they should be a sheriff of their thread if it's pretty apparent others would like to discuss tangents. I don't have a problem with a thread poster who ask others to start their own thread on tangents though. That can make the volume of threads on here a little unwieldy and hard to follow but, hey, most of us are pretty good at finding threads.
On the other hand, everyone who knows much of anything about this site and the posters on it knows Pat Mucci basically just likes to hear himself talk, and he's frightenly didactic which never makes for very dynamic threads when it comes to the responses and opinions of others.