It depends very much on the topic and the poster.
Let's just say that a topic, posted in General Discussion, is about something that asks people what they like (and let's say it's about puppies), then the discussion will more likely than not present a collective chorus of positive agreement. The very nature of this hypothetical subject will undoubtedly bring out the adoration that the majority of people have towards puppies [:dog:]. On the other hand, if we took this to, say, Mature Discussion, then we're prone to be on much more aggressive grounds. Members will then want to have their opinions heard, but some matters get to be pretty touchy. That should serve as a fine line for the puppy and a warzone. [jk]
In real life, the same could be easily applied to every person and every circumstance. If a person has had a bad day and wants to release some stress, they might come on the 'Net and try to do just that. And if they make snippy remarks, any reader would take that as them being rude, without comprehending that their day wasn't all that great. But this scarcely ever occurs, especially on these forums. The polite people seem to always be more prevalent than those who are plain and outright rude.
Lastly, forum moderation is only there if we need it. Otherwise, in the case that most of the members are rude, the requirement for some form of arbitration would be necessary so that the entire community didn't go down hill.