Lobste.rs (and some others) is living well without downvotes, so the feature is barely vital. It's rather a cheap means to remove work from admins and delegate it to pseudo random actors. Your view on upvotes is backwards. Mathematically it doesn't matter if you only have upvotes; it simply encourages a different, more positive behavior.
Reddit is mostly an example for what happens when rules and moderators are bad.
Reddit is mostly an example for what happens when rules and moderators are bad.