So my only piece of (hopefully) constructive criticism is that I think there's a prima facie less biased stance to take with an announcement like this. It might go like:
Dear HN,
HN, as a public discussion forum, is a dynamical system that's always "attempting" to spiral out of control. Hence, we have moderators. Our moderators can only inject so much stabilizing energy into HN, and we've noticed that many or most political discussions are more energized than we can handle. So, we're going to see what HN looks like from a moderator's POV when we disable political discussions.
I guess this too sounds a little alarming, but my point is that I think there could be a way to talk about the issue at hand in terms of pure magnitudes instead of using language that says anything qualitative about different types of discussions. Something about the idea that "we have certain values, these discussions aren't aligned with our values, these discussions don't belong here" is a little off-putting.
All that said, it's not at all ridiculous to test whether or not banning political debate may in fact make HN a more robust and effective knowledge hub. Hopefully this experiment will yield interesting results.