A troll pit is where sedentary trolls go to lurk and graze with their kind. Occupants of such places tend to be deliriously fanatical in a narrow sense, often celebrating vulgarity and syncopated nitwittery.
Some of the best examples are Atheists sites where groups of undereducated culties protect their ignorance by banning any challenge to their pseudoscientificly justified self righteousness.
Censorship is their main defense, assuming the initial tongue lashing doesn't do the trick.
I stepped into a troll pit the other day (shudders). The stench of it sticks on you worse than cigarette smoke. I suspect free speech is nothing more than a handout to those people.