Generally I feel Karma does a good job of keeping the comments in check.
I think the Wikipedia article was an emotive exception.
EDIT: Thought I'd add that there were a lot of positive and friendly comments surrounding the Curiosity landing. So I don't feel like the tone of comments is leaning in one particular direction.
The problem with Karma is that too often people are voted down for simply posting views others disagree with, and I didn't think it was for that. That that leads to is people not sticking their necks out and only posting if they agree with the community vibe.
Cards on table: I have often avoided replying through fear of people not liking my opinion, regardless of how well thought out it might be. Often only replied if I already know my views are acceptable here. In fact, to get Karma up, I have merely posted agreeable posts. For example, I have noticed that having a go at the MPAA gets lots of up votes. See what happens if you dare argue for the MPAA, you enter down vote hell!!!
That has to be badly wrong, right? Surely its is the worst sort of mob rule and utterly stifles diverse opinion. Is that what HN is all about?
However, I don't know of a better way to do it, so it is better than nothing.
I think the Wikipedia article was an emotive exception.
EDIT: Thought I'd add that there were a lot of positive and friendly comments surrounding the Curiosity landing. So I don't feel like the tone of comments is leaning in one particular direction.