I appreciate the risk that you're describing. Of topics sliding into non-constructive venting.
And I have definitely seen a few comments and maybe a topic or two that are fishing for emotional responses.
You will have more experience with this than I do, but my impression is that, on here, even those topics tend to largely remain calm and conversational.
What you're probably trying to prevent, is the kind of emotional outbursts that do nothing to add or at least invite constructive discussion material. But I haven't really seen that here - say, apart from a few sarcastic remarks on occasion. And as you mention, in most cases the topic is indeed brought back from the brink of insanity by the majority of "good" members (or those who aren't having a bad day).
So, I might be inappropriately lenient, not being the one feeling the moderator burden on my shoulders.
But I don't think I have seen anything in danger of derailing anywhere, yet.
Just to add:
There's always the question what to do with the more disruptive or unpleasant elements in any group.
On forums, what tends to work well is the "ignore the troll" advice.
And if the behavior isn't quite trolling, but still somewhat clouding the mood of the forum, a subtle and private hint is often very effective.
Otherwise, have faith in your community