Not sure about the downvotes on this comment; but what parent says has precedent in Cubby Inc. vs Compuserve Inc.[1] and this is one of the reasons Section 230 came about to be in the first place.
HN is also heavily moderated with moderators actively trying to promote thoughtful comments over other, less thoughtful or incendiary contributions by downranking them (which is entirely separate from flagging or voting; and unlike what people like to believe, this place relies more on moderator actions as opposed to voting patterns to maintain its vibe.) I couldn't possibly see this working with the removal of Section 230.
Theoretically, your liability is the same because the First Amendment is what absolves you of liability for someone else's speech. Section 230 provides an avenue for early dismissal in such a case if you get sued; without Section 230, you'll risk having to fight the lawsuit on the merits, which will require spending more time (more fees).
I'd probably like the upvote itself to be considered "speech". The practical effect of upvoting is to endorse, together with the site's moderators and algorithm-curators, the comment to be shown to a wider audience.
Along those lines then then an upvote i.e. endorsement would be protected, up to any point where it violated one of the free speech exceptions, e.g. incitement.
HN is also heavily moderated with moderators actively trying to promote thoughtful comments over other, less thoughtful or incendiary contributions by downranking them (which is entirely separate from flagging or voting; and unlike what people like to believe, this place relies more on moderator actions as opposed to voting patterns to maintain its vibe.) I couldn't possibly see this working with the removal of Section 230.
[1] https://en.wikipedia.org/wiki/Cubby,_Inc._v._CompuServe_Inc.