Political participants do not just have different norms of community participation: by definition, they have very different motivations as well. This is the real take-away of Politics is the mind-killer. Keep in mind that politics is a kind of conflict: it's about things that people actually fight over, in the real world. So the difference in norms may well be a consequence of these motivations: as the potential for real strife increases sharply, good deliberation becomes less relevant and "fairness" concerns are far more important:
This is why I very much agree with the spirit of this post: we definitely don't want to attract people who are just looking to win by diligently adding more recruits to their preferred side. At the same time, we can hardly afford to disregard the norms of political debate entirely; that's a recipe for being perceived as somehow "biased" and "unfair" by the general public when political issues do become relevant, despite our best efforts. IOW, the norms aren't really the problem. The best compromise, AIUI, is to cautiously encourage (1) the rise of factional blogs like More Right and Slate Star Codex as venues where folks can apply the skills of rationality to their favorite political perspective, while interacting "at arms length" with other sides, and (2) developing political mediation and conflict reduction skills at LessWrong itself, while keeping ground-level political disputes mostly off limits.
More Right doesn't allow comments, so how does that work?
(I hope that is the least click-baity title ever.)
Political topics elicit lower quality participation, holding the set of participants fixed. This is the thesis of "politics is the mind-killer".
Here's a separate effect: Political topics attract mind-killed participants. This can happen even when the initial participants are not mind-killed by the topic.
Since outreach is important, this could be a good thing. Raise the sanity water line! But the sea of people eager to enter political discussions is vast, and the epistemic problems can run deep. Of course not everyone needs to come perfectly prealigned with community norms, but any community will be limited in how robustly it can handle an influx of participants expecting a different set of norms. If you look at other forums, it seems to take very little overt contemporary political discussion before the whole place is swamped, and politics becomes endemic. As appealing as "LW, but with slightly more contemporary politics" sounds, it's probably not even an option. You have "LW, with politics in every thread", and "LW, with as little politics as we can manage".
That said, most of the problems are avoided by just not saying anything that patterns matches too easily to current political issues. From what I can tell, LW has always had tons of meta-political content, which doesn't seem to cause problems, as well as standard political points presented in unusual ways, and contrarian political opinions that are too marginal to raise concern. Frankly, if you have a "no politics" norm, people will still talk about politics, but to a limited degree. But if you don't even half-heartedly (or even hypocritically) discourage politics, then a open-entry site that accepts general topics will risk spiraling too far in a political direction.
As an aside, I'm not apolitical. Although some people advance a more sweeping dismissal of the importance or utility of political debate, this isn't required to justify restricting politics in certain contexts. The sort of the argument I've sketched (I don't want LW to be swamped by the worse sorts of people who can be attracted to political debate) is enough. There's no hypocrisy in not wanting politics on LW, but accepting political talk (and the warts it entails) elsewhere. Of the top of my head, Yvain is one LW affiliate who now largely writes about more politically charged topics on their own blog (SlateStarCodex), and there are some other progressive blogs in that direction. There are libertarians and right-leaning (reactionary? NRx-lbgt?) connections. I would love a grand unification as much as anyone, (of course, provided we all realize that I've been right all along), but please let's not tell the generals to bring their armies here for the negotiations.