The only counterbalance to this right now is admins killing topics. Doing that after a story has generated a lively discussion like this one might cause users to revolt.
Who cares about a "user revolt"? This site has a focus and that's what makes it great. Those people can discuss this stuff a million other places. There's only one place for hacker news.
A counterbalance to this sort of thing that works is a community action, not an admin action.
A one way to implement the community action is to add downarrows. But when someone downvotes a story, the story karma is unaffected. It's only when the story has more downvotes than upvotes that the editors get the option to kill that topic. So that way, the community has decided something is offtopic, but the editor still uses his good judgment about killing a story. I don't see how users could get upset under that sort of arrangement.
reddit.com
The problem is that the average quality of the politics discussions so far is much lower than that about startups. It's not "hacker-worthy".
Social news has been around for two years. Giving one example doesn't mean a whole lot, especially when the community of reddit is fundamentally different from the community of news.ycombinator. The editors of reddit believe in non-intervention. The editors of news.yc believe in active and regular intervention, which means that news.yc won't turn into reddit.
The discussion in this thread isn't anywhere close to what you see on reddit. We have a problem when discussions start actually polluting the site. But they haven't yet, so I don't understand what the problem is.
We need to consider exactly what we don't want to allow on this site. See my new thread.