I'm pretty active on 2 forums, Sony and Oly Compacts, on DPR photo site since 2012.
It shows up mostly from people who have a strong need to be right, and it comes and goes in waves.
When I first joined, late 2012 when Sony rx100 1" sensor revolution started, my first impression was awful, a few trolls, and people who strongly took the bait, added a lot of negativity. I could skip posts from those people, except, the people who took the bait, and the people who need to be right often do know a lot, so I took the good from the bad.
Then the trolls disappeared, it got quite good for a long time,
then, as a result of newer 'better' models, a few new, quite knowledgeable people joined, but stiff, my way or the highway ... I discovered, peoples professions sometimes set them up, they need/ed to be critical to succeed, then it becomes a life long habit. To the point of telling people not to post their photos.
Oh baby, private messages ensued, ... new understandings were found, ....
