The vote ranking system is good if you want a steady stream of new curated content and your taste largely coincides with the user base. For instance, you go to “r/catpictures” daily and find the most upvoted cat pictures that users have submitted for that day.
But the vote ranking system is absolutely horrible if you want any sort of in-depth conversation or to have multiple points of view. Conversations on forums might go on for weeks or even years, and people have time to dig up information, view media, ruminate on a point, etc. and come back and add to it later. If you don’t make a comment on a Hacker News post within a few hours, it’s likely that no one is going to read it. Come back a few days later, and you’re just shouting into a void.
Even if you do comment within a few hours, most people are going to just reply to the first couple of comments that were made. Very few people are going to scroll down and read the comments at the bottom.
And if a controversial opinion is split 52%/48%, it’s quite possible for all the comments that are in the 48% are downvoted. Even if one side isn’t 52%, but there’s a small but fanatical fanbase. IE, /r/soda is 10% coke fans that will downvote everything that’s pro-Pepsi, 15% Pepsi fans that will downvote everything pro-Coke, and 75% people who just don’t care. This will lead to all the pro-Coke posts being downvoted and all the pro-Pepsi votes being upvoted. Worse still, since Reddit and HackerNews only use the aggregate score, it will simply appear to most users like no one supports the pro-Coke position.
Of course, neither solves the problem that the most mentally unhealthy individuals are often the ones who spend the most time online, and they’ll be the ones who dominate either style of forum.