I've actually always thought that the Slashdot algorithm was one of the better thought out approaches. You cap it at 5, give it a reason. Good behavior is rewarded with the ability to vote for a short period of time so you have to use your votes with some discretion for what you REALLY think needs attention...and if you comment on a story you can't vote on other comments.
The Slashdot moderation system didn't start out great, of course; it was actually pretty simple in the site's early days: no cap on karma, karma scores displayed prominently everywhere, no meta-moderation, etc. Much more Reddit-like than the system in place today. Which turned out to be a disaster, as this kind of naïve scoring system is catnip for trolls. Over many years they slowly improved the system, with each improvement leading to a new wave of attacks by trolls looking for ways to defeat it, until it finally got good enough to make trolling unrewarding and the attacks died down.
All of which is to say that the current design of Slashdot's system contains an enormous amount of valuable information about how to defeat trolls. You could write an entire book on all the lessons Slashdot had to learn the hard way along the road to making it what it is.
Which is why it's so tragic that their experience has been more or less utterly ignored by the community sites that came after it -- looking at you, HN! -- who universally went with simpler, naïve systems like the one Slashdot started with, with the completely predictable result that they were as much a green field for trolls as Slashdot used to be. So much heartburn, all of which could have been avoided if we as an industry had an institutional memory that ran farther back than two or three years. What a waste.
You say it took many years to solve, but fact is they solved it over 10 years ago, before Facebook and Reddit and HN were even invented. Nothing open to the general public matches the moderation quality.
HN isn't bad, because of the technical measures that prevent comment spam and the admin moderation.
The calculation is likely that users do not participate as much if you increase the cognitive friction involved in performing an action. Having to select an explanation for the vote is absolutely a much heftier problem than just expressing the sentiment.
The issue is probably less in the interface presented to users and more in the way the backend accounts/tallies scores, and then uses that data to determine the placement of the content.
The "direct democracy" approach of just taking the raw counts and sending them through a pre-set formula results in groupthink and echo chambers, we know that. As you know, Slashdot's saving grace was not that they required posters to say "Insightful!", but that there was reasonable human curation supervising the system.
Reddit takes a laissez-faire approach to moderating content, leaving it in the hands of subreddit moderators, and afaik does not attempt to modify non-spam vote counts (except for a few exceptional subreddits).
While you could definitely write more objective algorithms for ranking content, the question is really "Content is better according to whom?" Because the fact is that most people do not want to hear from the other side. You will not have a successful community where one story is "Vote for Trump" and another is "Vote for Clinton". You will have factions that try to tear each other apart (reddit is also an example of this, but not because the ranking is trying to be fair).
Not only do most people not want to be "open-minded", aka "experience and suppress cognitive dissonance until it's rationally justified", most people are frankly incapable of doing so. They do not subscribe to the FB pages of both Local Dems and Local Reps because they like to know both sides of the issue. They subscribe to one or the other, or neither, because they've selected a tribe and completely intend to stay with it. Information contradicting or deriding their tribe is a vexation, and they won't tolerate it.
The implication for content ranking is that if you want an intelligent ranking system for interesting, challenging, or in-depth discussion, you want something completely different from what the public demands.
And that really gets at the crux of this whole issue. We look at "native ads" promoting fake dating sites, penis enlargement pills, and gambling, and we scoff. These work because many other people don't scoff, they say "Yes, I want sex and money" (and who can really blame them?). While they may be socialized to be embarrassed about it, they take advantage of the privacy the internet offers them and click anyway.
Now the question is, you have a business that has to make money. Like it or not, which market is the better target? The discretionary, measured, judicious reader, or the person who will impulsively click through to a site promising him an elongated penis?
