A big part of it is how the site is moderated. Another site I visit has much stricter moderation as is a much nicer place as a result.
When you have people getting away with being aggressive and rude, and are not picked up on it, the forum becomes a free-for-all. In the majority of cases, threads are only closed when they have turned into a multi page slanging match.
Some people need to be told that they shouldn’t speak to people in a certain way and if they continue to do so they will be banned. What happens is the people who cannot behave get banned and those who want to stay part of the forum get in line.
STW is a great resource and there are lots of good people here, but it is let down by the moderating.