I would imagine that this (admittedly plausible-sounding) scenario is offset by the fact that, given the audience, a politically-motivated DDOS would have the opposite of the desired impact. No one here would cheer the loss of HN, even its critics (like me.) We want it to do better.

It's simply too valuable for either side to destroy.

Generalizing, it's not a belief in unfettered free speech that saves us but rather a belief in carefully curated conversation. The archangel Dang keeps the discussion so valuable that there is no margin in damaging it.

If the tenor of the conversation declined to the point where it was a Twitter-grade dumpster fire, then yes, someone would eventually DDOS it.