I’m honestly probably gonna lose a follower or two for the next sentence, but at least read my whole reasoning before you do: I don’t think the reason for Captain America: Civil War happening should have anything to do with Bucky Barnes. Should he be in it? Definitely. Could he be a minor plot point in driving Tony and Steve apart? Sure, why not. Whether he was in control of himself or not, he did kill Tony’s parents, and Tony has a right to be upset about that. Should Bucky be a main reason Civil War happens, and causes an extreme rift between Steve and TonyNo.
First of all I think that they would totally fuck up Tony’s character. It makes Tony seem hypocritical and like he’s not owning up to the mistakes of his past. Tony wasn’t always a good guy. Was he a villain? No. Is Bucky a villain? No. Did Tony do things he isn’t proud of? Yes. Did Bucky do things he isn’t proud of? Yes. Did Tony’s inventions cause the death of thousands, making him feel indirectly responsible for the death of said people? Yes. Did Bucky’s actions lead directly and indirectly to the deaths of hundreds, if not thousands of people, even if it was his conditioning that made him do so? Yes. Does Tony feel guilty for it? Yes. Does Bucky feel guilty for it? Yes.
And I’m sure there will be people who tell me that it’s not the same, Bucky was brainwashed and Tony was not. But I feel like if they make Tony not trust Bucky because of the actions of his past, that would destroy Tony’s purpose as a hero in MCU. Tony realized what he was doing was wrong and stopped. Bucky was released of the brainwashing and stopped himself from going back to them, and from killing Steve. Making Tony not trust Bucky because of the things he did and the people he killed would, to me, make it seem like Tony isn’t owning up to the fact that he, directly or indirectly, is responsible for the death of human beings. Because Bucky is also not directly responsible for the death of the people he killed. Just like Tony isn’t. And having Tony say “I don’t trust you, even if you’ve changed, because you’ve killed people in the past” would, in my opinion, ruin what they have done for Tony’s character so far. He didn’t shun Bruce, even though the Hulk undoubtedly killed hundreds of people, for the Hulks actions, because that wasn’t Bruce’s fault. And it’s not Bucky’s either.
Another reason I think that Bucky shouldn’t be a direct reason for Civil War is because I think the movie Captain America: Civil War should be based off of the comic Civil War. Sure, you can’t follow the plot exactly: Spider-Man won’t be in it to unmask, they don’t have the rights to The Fantastic Four to make Richard a complete dick, half of the characters haven’t even been introduced, and they don’t have a Ragnorok to kill Goliath (yet). But, the main plot point still stands. Something happens because of heroes (whether it be the school blowing up like the in comics or Ultron have scared the shit out of the world - cause you know, collateral damage in that was like wow) and the government enacts the Superhuman Registration Act. Tony sides with it, Steve doesn’t, Avengers and heroes are divided between the two and battle happens, hence the name Civil War. (I’m also pretty sure at this point that they plan on having Agent 13 and Crossbones kill Steve like in the comic.) AND THAT WOULD LEAD RIGHT INTO TONY’S SPEECH FROM CONFESSIONS, HEY MARVEL, LOOK HOW EASY THAT WAS.
Also, Bucky wasn’t even in Civil War that much, or like at all that I can remember, so trying to force him in and make him a super important plot point would be dumb. I get that you want Steve-Bucky interaction in there but please, don’t ruin the whole movie just to fit it in there.
(Sorry. Civil War is my favorite comic and I have so many feels about this movie. If they completely fuck it up I’m gonna be so pissed. When this movie comes out I’m going to be judging it so hard.)
Update: I did lose a follower. Oh well.