The unfortunate fact is that political discourse in America (and, I understand, in many places elsewhere), has been reduced to lizard-brain questions.
In particular, but certainly not as the only example, the US president-elect ran on a platform that many of us would characterize as playing off machismo and fight-or-flight, rather than actual policy proposals.
HN is a good thing not because it's a way to waste time at work, but because discussing technology ultimately helps us create better technology. But the assumption in this decision seems to be that discussing politics doesn't help us make better political decisions.
I think it's clear to most of us that tech's recent success is due in large part to communities -- open source, StackOverflow, and yes, HN. We learn from each other, and this makes us all better.
If we think this model doesn't apply to politics, that each of us is better left to make up our minds independently, and that we cannot learn from each other, I fear for the future of democracy.