Right, from a user's point of view labelling it "Spam" has the same effect as when you put letters unread on that pile by the door, "I don't want to read this". Should they? Doesn't matter. Years back we even had users who were paying us to send them specific emails and would mark it as spam.

The use of "users marked this as spam" as a signal is a cheap but lousy shortcut and it's bad news that we became reliant upon it.