You're right that HN should be a place for intellectual curiosity and substantive comments. But here's what I've seen in the past year:
* Flagrantly allow anti-prop-8 posts and submissions to assist in the smearing of Brendan Eich.
* Flagrantly allow pro-clinton posts and link submissions to thrive on HN.
* Never step-in to stop downvoting brigades on pro-conservative/libertarian/tea party posts.
* After unpopular (with silicon valley) president is elected, ban political conversations on the site.
I won't call you biased, because you've been a damn good mod, but this is probably your worst decision, because it looks like sour-grapes-in-retrospect.
Perhaps you're doing it because the pro-clinton camp is actually becoming too toxic to tolerate. Perhaps you're doing it to avoid the 4chan brigade from promoting Trump. Either way, this is a site full of people skilled at reading between the lines, and, correct or not, this action doesn't look like a way of promoting reasonable discussion.