because it has 1000+ votes and isn't that old but is dropping off the homepage.
Compare the relative position of other threads and their upvotes and ages. There are older threads with far fewer upvotes that are higher up on the page. That implies flags. The fact that this thread has 1000+ points and is this low means it must have been flagged extremely heavily.
Ah.
Hm, I guess I should delete this submission. The Slate piece does seem to be subsumed by the Guardian.
Quite the opposite. You should leave it to offset the flagging of the other thread.