Yeah here's the problem. Let's look at a site like neogaf, ever wonder why at one time it was the place to go and developers would post there and people would leak information. And now developers don't? Active participation is down? It was the moderation as you pointed out, but let's look at their definition of a troll, which basically boils down to "anyone who doesn't subscribe to the narrative." Let's look now, at what will get you banned. Have a contrary view of feminism? Banned. Support some ideas of a MRA? Banned. Have differing view points on global warming? Banned. Prefer the xbox vs playstation? Likely banned. Don't like your vidya characters to look like they were hit with a bat? Banned.
The problem is in many cases, moderators especially in this day and age use that as a form of power projection. A good example of this is /r/politics or /r/canadapolitics where you have moderators who ban people for pointing out factual information because it goes against the prevailing group think. Have a nice article about how forums become infiltrated by people pushing authoritarian viewpoints.
I ran a BBS in my teens, and it got large enough that I was considering applying for a regional fido:net hub. At nearly 700 people and 4 nodes, I picked moderators for my forums who weren't assholes, who usually worked, and if they stepped over the line they were given one warning then booted. As sysop, I expected my mods to be impartial. And if a friend was involved to pass the issue to another mod to deal with. I ran on Renegade.