Occasionally commenting on a political issue isn't a problem as long as you do it civilly; some overlap with political topics is unavoidable. But when political battles become the thing you're primarily using HN comments for, that's when it becomes abusive.

HN's purpose is the gratification of intellectual curiosity. We can't be that and be a political battlefield at the same time, so we need to draw the line somewhere. The 'primarily' test turns out to be a good place to draw the line.

(There's a separate question of what kind of comments people post when they do turn to politics. To the extent that an account does political flaming as opposed to thoughtful discussion, we adjust the line in favor of more moderation.)

See https://news.ycombinator.com/newsguidelines.html for more.