We can't exclude politics altogether, nor would we want to. But we can't let it take over the site either, and it's like fire: it consumes everything it touches. This is a conundrum. Our way out of the conundrum is the 'primarily' test:
We ban accounts that use Hacker News primarily for political or ideological battle, regardless of which politics they favor. https://news.ycombinator.com/newsguidelines.html
We noticed that the most damage comes from users who don't care about much except their politics, while users who are interested in plenty of different things and occasionally post on politics tend to be benign. The first group is abusing the site while the second is using it as intended. That turned out to be a clear line that we can rely on as a standard for moderation.
We try to warn people first, especially when they've been on the site for a while, but if the pattern persists we do ban them. So would you please reread the site guidelines and use HN in the spirit of curiosity, not battle, from now on?