why do so many discussions turn contentious?

Needless to say, the phenomenon is hardly confined to this forum. Fundamentally, most users of internet forums behave very differently than they would in person. By way of analogy, I find this brief Louis CK bit to be both on point, and very funny:

https://www.youtube.com/watch?v=x8062QEFk5g

Nothing wrong with disagreements, of course, but how people disagree can make an enormous difference in how conversations unfold, and culminate.

Showing restraint and being polite can be a challenge for many. I have struggled myself at times to dial back aggression, be more patient, and avoid coming off as arrogant. The simplest tool that I have found is to stop and think about whether I would say whatever I am about to post to the face of the person to whom I am responding. If the answer isn't an easy "yes", I'm inclined to edit, and dial back the response.

It’s a good question, OP, why some feel a need to create contention and acrimony, especially when the thread is about a fairly innocuous topic.

The need to react (as @oldhyvvy pointed out) is now leaps and bounds beyond where it was. Everyone needs their squirt of dopamine, and rather than remain silent about a topic about which they’re ignorant, they poke at others. Gotta get that reaction. It seems like they know what they’re doing, but it’s a chemical addiction, under the surface.

Then again, it could be a kind of self-loathing, frustration at not really having something to contribute to a topic, but unable to resist the impulse to get in the mix, anyway. Causing trouble out of boredom and perhaps inner frustration with their own lack of information, insight, intellect? These are the posters who "blurt" things nearly all the time. I imagine them in the stands at a sports game, yelling stuff. Nothing more rattling around their head except the last Big Gulp soda.

(As long as we're quoting famous authors, Nietzsche called the attitude 'ressentiment.')

"A vengeful, petty-minded state of being that does not so much want what others have (although that is partly it) as want others to not have what they have….Ressentiment is more fully defined as the desire to live a pious existence and thereby position oneself to judge others, apportion blame, and determine responsibility."

Through technology we have become an impersonal world where minimal face to face human interaction dominates. Basic manners are not required.  Heck, the basic respect and civility required for face to face interactions barely exists in the real world anymore, and definitely not on this or other forums.  

There are very few forums that do not devolve into name calling or cheap shots. There are no consequences for doing so.  Everyone involved in name calling or posting cheap shots blames the other posters.  I cringe as I read some of the posts on this forum. Every hobbyist forum is populated with persons that came to that forum in the first place because of the same interest.  So stop the cycle. Post your opinion respectfully without the cheap shot.  Simple.  It applies to everyone on the forum.

 

Here are some quotes to ponder.

“Through a vicious circle of pure reason skepsis itself becomes dogma.”  Johann Georg Hamann German philosopher

“No man burdens his mind with small matters unless he has some very good reason for doing so.”   Arthur Conan Doyle

“The reason that university politics is so vicious is that the stakes are so small.” Attributed to Henry Kissinger.

 

Apply any of these quotes to any hobbyist forum. This forum is not alone in the devolving rhetoric. Only we can change it.  Not the moderators.

First, I have to send a BIG THANK YOU to whipsaw for that hilarious Louis CK bit! In less than 3 minutes that bit summarizes most of the ills of humanity, many of which have been touched upon in this thread. Humor is, often times, the best teacher.

With regard to the original premise, however, I guess I respectfully  disagree. Maybe this is because I'm a relative newbie to this forum and haven't encountered anywhere near that level of contentiousness in the threads I've followed. Thus far, for the most part, I've found this forum to be very helpful. I've received generally good, well intentioned guidance from folks who genuinely want to be helpful and selflessly share their experiences and expertise. Sometimes, that guidance and assistance has been outstanding! There are, of course, those who are occasionally snarky, bad-tempered and not inclined to lend assistance at all; those who just want to crow about the superiority of their equipment and their perceived expertise and/or intelligence. In so doing, folks like this accomplish nothing other than exposing their inferiority complex.

Audio opinions are like a**holes, everybody has one. And being semi anonymous noboby is afraid to voice their "ideas".