IIRC it's unlocked at 500 karma. You need to contribute in ways the community considers valuable before you can signal that something isn't valuable.
Yeah I wasn't sure of the actual threshold (I kinda just lucked into a lot of karma early on because of a post about factorio releasing 1.0)
Ah, that makes sense. I'm basically the opposite, in around a decade I've posted articles directly maybe a dozen times, so it took me a while before I received the privilege to downvote.
I only see downvote sometimes, for some reason. I don't see it available on the comments on this post.