From a British perspective, I find most of the political discussion on HN to be useful, although perhaps I just instinctively avoid some topics. There are a lot of global issues which are being discussed, whether that's climate change, transport, tech and data regulation, job automation, money in politics, licensing and intellectual property, electronic surveillance, global trade, etc.
These are all issues which are relevant to the technology community, as big social issues which are targets for innovation, as moral issues which we have to grapple with, or as concrete barriers which directly impinge on us. I'd say having a space for the technology community to discuss these things is a source of a fair amount of the value of this discussion board.
Having said that, political discussion does have to be subsidiary to technology discussion. Once political discussion gets over a certain level, you're just appealing to a general audience and the forum loses its distinctiveness.
So I sympathize with the moderators. You always have to draw a line in the sand, unfortunately attempting a total ban is going to be just as subjective as what goes on at the moment, which is moderators removing or flagging thread-by-thread (presumably to avoid general topics dominating, or to kill off those particular comment threads which have become toxic). I suggest they just keep on muddling through, and we just acknowledge the process is necessary but messy, and cut them some slack.