That said, a downvote, or a "dislike" button, is almost always a double-edged sword - although it can be used to tune out hateful comments, it can also turn potentially meaningful comment sections into echo chambers extremely fast.

I do not see this turning out well.

I have a sense it will only worsen the mob mentality on Facebook and make it more like Reddit.

Is like meant to signify I agree with this comment. And dislike means I disagree with this comment or does dislike mean I think this comment is bad, O/T, abusive. Or does dislike mean something else.

What if you disagreed with the comment, but felt it was a good comment, well argued, well presented and fair etc. would you like it or dislike it?

I feel "like" would make it look like you align yourself with the poster, which you may not want but dislike seems wrong too.

Maybe overall like / dislike is an indicator of quality of comment, regardless of your personal alignment with the content?

I don't get it.

Say what you will about echo-chambers and stuff associated with comment voting, but IMO reddit/hn are orders of magnitude better than fb.

(1) I don't think that's the case, and

(2) Facebook's selling point to users has never been on being a neutrally optimized discussion site, it's been on algorithmic optimizing to show you what you want to see. Having a negative interest signal quite reasonably improved the data available for that optimization.

> and that downvoting is always used as a "I disagree" button?

Whether or not that is generally either true or desired by other sites implementing comment voting, given the nature and focus of Facebook, I absolutely do think that use of a dislike (not “downvote”) button for disagreement is perfectly consistent with Facebook's likely intent in implementing it.

Additionally I think the best option is to completely hide the downvotes from other users, especially in the score numbers. Ideally you don't show the score to anyone but the comment owner.

On Reddit, once you dip below 1, people tend to simply vote down even more. Not because they disagree but because it's a bad comment. It must be, it's score is negative. From what I've observed, controversial comments (when marked as such) are usually the ones that have initially gotten enough upvotes to stay positive through the downvotes.

Hackernews also has (IMO) some signs of downvote trains where people downvote comments with the shadow but HN usually quickly hides the comment or dead/flag marks it to prevent further voting.

In an ideal system I would also not simply rank by the score or a variation of it. I'd spray in some controversial or low-ranked comments into the high ranking ones to ensure that people with not enough votes get visibility even when the discussion has been going on for a while.

Personally, I don't find anything bad about a downvote existing, it just needs to be carefully gated and manipulated so as to decrease the usage as a "I disagree" button without people wanting a "I disagree" button nor that vote brigading/raiding becomes a problem. Furthermore I think it's important that people don't have the score of a post so as to improve the neutrality of presentation.