RE: the question: ":Why do forum interactions become contentious". . .

Some folks get so emotionally invested in their opinion that they perceive challenges to their opinion as somehow challenging/insulting themselves.  I suspect many anti-cable folks fall into this category and are so emotionally entrenched that they cannot emotionally look at evidence to the contrary.  Many of these folks experience emotional pain when they admit they’re wrong so avoid it at all costs.  The truth is that varying opinions leads to debates which help us to learn and grow.

Always look at the bright side. It beats shooting each other. 

It’s a great philosophy.  An attitude of gratitude leads to a joyful life.  Too many people focus on what’s wrong with the world which isn’t healthy mentality.  If one focuses on the news, which is heavily slanted to the negative and entertainment ratings, will lead to a negatively balanced point of view.
The good news is that people can change for the better.  How?  Thinking is nothing more than asking and answering questions. Negative people are constantly asking themselves “what’s wrong with ___”.  So asking better questions such as “ what’s great about this, what can I learn from this, what I am grateful for” creates healthy thinking.  Also, intentionally changing focus from a negative to a positive also greatly helps one’s mentally.

I get the topics email every day and I check in on this forum but I don't spend much time here. There seems to be a high level of dysfunctional interaction.

I have had a much better experience with the audio forums on Facebook. They are much more tightly moderated and a**holes are removed pretty quickly. I also like the structure better that allows you to efficiently respond to individual posts in a thread. The overall level of ego also seems to be less. People generally want to share information and help each other.

I used to have a recording studio and there were some recording forums that were as bad as Audiogon. Gearslutz was the best example. You could always depend on a few jerks mucking up any good discussion.

Audiogon is worth a quick scan every day and there are a few threads like Thiel Owners have been extremely valuable and constructive. I paw through the trash to find the occasional diamond and try not to waste too much time in the process. 

As I recently posted in the cable debate thread,

"The conflict occurs when people need others to share their same beliefs"

Disagreements (about audio stuff) are often interesting and particularly when folks offer well thought-out arguments or personal observations to support their positions.  These forums would be boring without opposing viewpoints.  Having confidence in one's beliefs is fine, just keep the discussion on topic and tolerate those who disagree.   The consequence of not keeping disparaging remarks and personal attacks in check will be less participation on this site by potential new members and by others who do not want to put up with the antagonism.  Audiogon can decide what they want to tolerate, and then live with the result.

For what it’s worth, I participate and contribute to more than a few audio forums. The only forum that tolerates contentious and confrontational exchanges with regularity is this one. 
From what I have observed, confrontational  exchanges tend to be a feature, not an aberration, on this site. That is unfortunate, because I enjoy and appreciate much of the non-confrontational input I’ve received here.

Personally, I believe that the moderators and sponsors of this site intentionally, if passively, promote no-holds-barred discussion to differentiate this forum from others.