Its not really flagging. Its a downvote, just like in reddit. The flag is something that they made up for the UI to discourage irresponsible use. There's not even any proof its a flag. That picture could be an empty box of tampons with a pencil sticking out of it.
If you want to think of it as a thumbs down (which is how its expressed on steemd.com) then you can do that too.
But, in the actual back end, it is a vote, just one with a negative weight.