1. Robert Downey Jr's Tony Stark Just Wouldn't Do That
Robert Downey Jr's interpretation of Tony Stark/Iron Man is the undisputed backbone of the Marvel Cinematic Universe. RDJ breathed new life into a character who was once so unpopular, his comic series was almost cancelled by Marvel. This is an Iron Man who is funny, quirky, a little obsessive-compulsive and definitely anti-establishment. The thought of this genius, wise cracking anti-hero suddenly becoming the government poster boy for the militaristic superhuman draft is...just...ludicrous. Throughout the Civil War books, Tony Stark is nothing if not a serious, focused man. Basically, he is nothing that makes the MCU Iron Man so fun to watch. Gwyneth's Pepper Potts would never let RDJ act the way Iron Man does in Civil War. Of course, in Civil War, Pepper Potts is actually dating Happy Hogan. Did I mention (spoilers) Happy dies in Civil War? Yeah...and Tony is the one who pulls the plug on him. To recap, he would have to team up with an evil-ish version of S.H.I.E.L.D. and eventually become the director. He would have to give up Gwyneth Paltrow to Jon Favreau, kill Favreau, almost kill Captain America, then abandon the Avengers we know to start a new team of "registered" Avengers. Come on...Robert Downey Jr's Tony Stark just wouldn't do that.