Tenacious, thank you for giving examples. In reading through them, I find some went over the line in making a point, but others I don't see the problem. I don't have the context, so it's hard to know on some of them
For example
It's somehow comforting to see that stupid posters are still proud of their ignorance and still posting away, proving stupid is something we can't fix, like a mental disorder
I feel this comment went too far. If it were my forum I would probably not allow that kind of thing, because it is insulting the person, not the comment, but it's not my forum. But as Simon pointed out, it is a discussion forum, if you cannot handle criticism, you should probably not be discussing your beliefs on it. I also don't know the context, perhaps the person was being deliberately obnoxious, I've seen some pretty stupid things posted here.
I always make sure that I can back up what I post. You're lack of ability to do the same is not my problem.
I don't see the problem here. There is no name calling, the person is simply pointing out that the person did not prove their point. The tone was a bit insulting, but if we didn't allow that kind of thing there wouldn't ever be any discussion of weighty topics. There isn't a forum on the internet that doesn't have that, most are a lot worse.
I have criticized other in the past for being insulting, but then I noticed that those getting the most ridicule were often people who refused to engage in any meaningful discussion, they simply wanted to spout nonsense and not be challenged. That isn't going to happen here and I wouldn't want it to.
All ideas and opinions are not equally valid. What the insulting posters are trying to do is to make people think, and to do that you sometimes you have to be blunt. If it distresses you to read that kind of thing, then you should stay out of controversial threads, or go to a different forum, there are plenty of them out there. I personally don't usually like insulting people, it's not my style, but I do think those people who do that often have very valid points. It might be good to just read their posts, with out any judgement about tone or manner, and see if there might be something for you to learn.