The up/down vote system directs the ranking algorithm on how to order posts and comments, and it visually signals to the user the relative popularity of a comment.

This, imo, is a wildly underappreciated mechanic for combating a lot of the harmful issues people associate with social media.

Most people recognize that discourse on Facebook, Twitter, YouTube, etc. is designed to divide and inflame people. the reddit-style downvote is remarkably effective at addressing this:

It does two key things in particular:

1. Downvoted comments are down ranked and hidden, so people are exposed to less toxic content.
2. If people do engage with unpopular comments, the negative score influences how people engage with them. On Facebook, commenting to defend Biden's Israel policy will get elevated and create viscous fights. On Lemmy, it will get flagged with a virtual dunce cap. You can dunk on it, but there's no point in arguing with it: we can all see that the argument is already over. Laugh and ignore.

Taken together, these discourage people from feeding trolls, and in doing so reduce the incentive to post something uncivil or stupid. It's a remarkably powerful tool to address a huge problem, and I wish more people understood this.