It has to do with us noticing an uptick in two undesirable things: harsh ideological comments, and accounts that use HN primarily for political battle.
You can see one example of how the idea developed here:
One of the things I've found most impressive about HN, in fact, is the fashion in which people disposed across the full width of the US political spectrum seem able here to discuss potentially divisive subjects in a civil and perhaps even constructive fashion - I can't speak for anyone else, but I can say that comments here have given me pause for thought, and on occasion to significantly reconsider opinions that I've held - not all of which I still do. This isn't to say that I'm politically progressive or at all likely to become so, but I have found uniquely valuable some of the political discussion which has occurred on HN, and the degree of dispassionate consideration and tenor of general civility I've seen in such discussions here are unique in my experience.
The point I raise isn't that I think the "political detox week" is a bad idea. (Or a good one - time will tell.) But I do think it would be a shame if political discussion were banned or severely curtailed on HN in future. Such a decision seems to me as though it could only be a deliberate effort to invoke the "echo chamber" effect which has redounded to such cost throughout US politics in recent years and especially in recent months. That's something I've seen happening to a broad extent on both ends of the political spectrum lately, and especially since the election. No one on either side seems willing to hear anything from anyone on the other - except here, and I think there's value in that.
Perhaps I'm alone, or nearly so, in this opinion. But perhaps I'm not, too. And even if I am, it still seems worth throwing out there. In an increasingly polarized political environment (and I say this as a veteran of the 2000 election and all that followed it!), HN seems as close as anything I've participated in, seen, or heard of, to a demilitarized zone where parties on both sides can meet and interact in something approaching a constructive fashion. I realize that's not HN's intended purpose, and I don't blame the mods here if they decide that's not what they want to run. But I do think it's something that'd be a shame to lose.