Reddit's voting system has two issues:

(1) Lots of strategic downvoting. That's why no thread stays above 75%. It happens to comments as well as threads. Some of it is spammers trying to improve their own ranking, and some is probably just trolls.

(2) "Stalker" downvoting, which is when a person retaliates to a comment by downvoting that person's contributions en masse.

I wonder if they've put any machine learning muscle behind this. Is it easy to fix, or is it just a hard problem?

The entire concept of the downvote is flawed and is very likely to be the absolute worst part about reddit.

In theory it may be a good idea, but in practice it's essentially a "CENSOR THIS POST" button that people use to get rid of content they don't agree with.

I've also noticed that negative points on a post completely destroys credibility despite cited evidence or a well thought out argument. I've seen identical comments on similar posts in the past where the first few voters determined the post's fate in that if the first few voters voted it down, the post would receive flames and even more downvotes, but if it was initially upvoted, more people would upvote it and it would receive well thought out replies.

Probably the most horrifying part of the downvote is that all it takes is 51% of voters to dislike your post to destroy it. For example, all it takes is 51% of viewers on the politics subreddit to turn the the /r/politics frontpage into a pseudo fox news where every single post praises democrats and slanders republicans.

It strikes me as disgusting that some people actually consider reddit to be a good place to have a controversial discussion when it's so pathetically easy to censor opinions that you don't agree with.

Each subreddit has different character, depending on the mods and the community that it attracts. Some skew one way, some skew another.

Hmm, very different perspectives; personally I think a big advantage of reddit over hn is that on reddit, if I see harmful bullshit or toxic garbage, I can do something about it without having to take up everyone's time. I don't downvote based on mere disagreement; surely there are some people who do, but I haven't seen that much of it.

That having been said, I mostly read the programming section of reddit; I'm prepared to believe standards might be lower in e.g. the politics sections.

Actually, (1) is the result of vote fuzzing by reddit. They intentionally manipulate upvote and downvote numbers to obscure from potential voting rings whether their votes are effective.

There are also some small safeguards in place against (2). If you literally go to someone's user page, and start downvoting every post, reddit will start ignoring your votes towards that user in actual score calculations.

Also keep in mind that Reddit throws in spurious downvotes as part of their spam prevention. For example, you may have a comment with 100 upvotes and 50 "downvotes", but in reality, most of the downvotes may be fakes generated by their spam prevention mechanism.

> (2) "Stalker" downvoting, which is when a person retaliates to a comment by downvoting that person's contributions en masse.

This is why downvots (or upvotes) are not registered if you vote from the user-page.

I feel like (2) isn't difficult, in absolute terms, but is simply computationally expensive. Reddit is _still_ crashing all the time. They certainly don't have the resources to throw a bunch of machine learning or algorithmic muscle into preventing downvote spam.

I don't doubt these are real issues on reddit. Even with that, good content does rise to the top most of the time.

As to the ops questions: you should look into creating a list of subreddits that cover these things you're interested in.

Please explain how it is a problem, let alone a hard one. Karma is a game played by whatever rules the players want. Reddit content is decently well correlated between how close a post appears on the top of the page, and how worthwhile that post is to read.