My mental model of downvote systems is that systems without them allow more diverse thoughts. Imagine a topic where everyone feels compelled to vote, skewed about 51% to 49%. Without downvotes, your top comments are going to be a mix of both sides. Opinions are about 50-50 and comments will look like that. It will feel frustrating, like in the article, because you see about half of these posts from those evil Others,…
Afaik, reddit has a pretty stable upvote vs downvote ratio, like 7:1. (Sorry, no source, but I remember the reddit founder saying it in an interview).
And in your calculations you assumed that every post receives the same number of votes. Also that is not true, because of ranking. Higher ranking posts get more views, more votes, more views and so on. In this case the upvote-downvote difference is different for two posts with different popularity, but same upvote:downvote ratio.