Style over Substance
Many boards employ strict rules about manners. Such policies can and do lead to high bullshit tolerance levels due to "everyone being entitled to their opinion" no matter how stupid the opinion is. A participant can post an idea as retarded as “the sky is red” and no one is allowed to point out said person is obviously an idiot.
Trolls often use such policies to their advantage to ignore arguments they can't handle because they weren't worded to the trolls personal standards of politeness. Said trolls will often post arguments containing politely worded but still condescending remarks, goading their opponent into openly flaming them. At that time, the troll can accuse them of breaking forum rules. The troll then declares him/herself the de facto winner of the debate, regardless of how sound or unsound their actual position is.