The only thing I could find in https://www.facebook.com/communitystandards#fraud-and-spam which justifies marking steemit links as spams is "We also ask that you respect people by not contacting them for commercial purposes without their consent."
Are they keeping it so generic so that they can throttle links to their competitor websites as well? :P I doubt that they would stoop down so low.
While I see your point I think your claim is a little exaggerated that facebook is doing that on purpose. It is just my opinion, but for all we know you could be right :)