Two main problems: 1) everything is politics and current events. That is, everything touches in some way on what's going on in the world and how you feel about it. Maybe I'm applying too broad a brush, but I can see politics and current events in every post on HN -- and always have. About the only exceptions would be the driest of technical articles. If you want a board of Erlang innards, go for it. Other than that, it's always going to be Steve Jobs, EFF, which VC trashes which other, etc -- all gossip. (And gossip is just a broad term for current events and politics)
People post, comment, and vote based on emotional response. You can pretend to cut that out by banning, say, any mention of political parties or politicians, perhaps any pending legislation, and past legislation, how economics prevents or helps startup creation, etc -- but I think you'll just trade one monster for another.
2) I've been thinking about this for a while, and the key problem here is that the commenting system promotes learning how to fit into a community of hackers, not actually doing anything useful. We think of the system as being some sort of logical function to take all kinds of input and provide the "best" stuff for hackers, but it's exactly the opposite: it teaches hackers how to get votes from other hackers. In other words, spend 3 or 4 years on here, like JacquesM did, and if you're lucky you become an expert on what to say and do to make large groups of hackers agree with you. The karma system and large crowds isn't training the material to be more targeted to hackers -- it's training hackers on how to target other hacker's response with their material: how to fit in, what to post to get a rise, how to succeed without really trying, etc.
You can blame the topics for being too emotional, but I think it misses the point. We've always had all kinds of issues on here. What we're getting is a larger pool of people actively gaming the system in hundreds of ways: what kinds of snide comments might sneak by, what's the best time to run flame-war submissions, who to praise, what topics to champion or deride. That's a function of forum size, not system parameters. And that's not even getting into the fact that with a large enough audience, somebody is going to get pumped about just about anything that appears on the front page.
There's nothing nefarious about this. It's all just people being humans. After all, if you are in a conversation, do you speak in order to provide factual information? Or do you speak based on your current emotional state and to effect the emotional state of others? Why would we expect HN to be any different?
Nyah. That proposed rule -- if you could somehow miraculously define it with the precision required -- wouldn't give you the results you desire.