While this is true with Facebook, Twitter, YouTube I think reddit algorithm wasn't designed that way.
The three sites I mentioned don't have option to downvote (well, YouTube removed it recently) this is purposefully done so anything that is controversial will drive engagement. People like to show disapproval, since there's no downvote in case of Facebook they will likely use the laughing emoticon or write a nasty comment, in case of Twitter or YouTube they will do the same. There is activity, those posts will be promoted and engaging even more people.
In reddit you could downvote a comment or even report it to moderators. The comment it will make it go to the end of the list and even collapse it. If moderator gets involved the comment will be even removed and a nasty user possibly banned.
This actually moderates the community. I noticed that on reddit the most hateful communities actually need moderators to tip the scales in the other direction.
This is why I'm not fully convinced that beehaw.org and tildes.net made a good choice blocking downvotes, as this requires more work from the moderators and prevents community to moderate itself. Though at least tildes.net has labels, which maybe do this function.