There's a karma threshold before you're allowed to downvote.

Could you tell me what that number is?

It goes up over time. Right now it's around 500.

For comments or posts?

Comments. I believe the threshold for flagging submissions is 1000, but I'm not sure; I didn't notice when I hit it. You cannot downvote submissions.

Flagging is considerably lower, this account can flag comments and submissions so I think ~20 karma is required to flag.

So you want to downvote his objection on the over hype in the blog?

No, I want to down vote comments that only serve to project a vague superiority vibe and don't add anything to the conversation.

Pointing out a blog post overhyped is useful.

Fair enough. That's not what I took from the comment though.

Your karma must be above 500.