It might just be me, but when Tony says that whole supervision thing in the trailer for [Captain America: Civil War](tag:994409), it sounds very personal. Yes, he did just create a genocidal robot, but he also helped create Vision (and c'mon, that alleviates a little of the guilt). Look at Bruce Wayne, following the death of his parents he turns into a giant-freaking-bat! Tony lost his parents when was what 21, meaning 25 years have passed - and yet Tony just found the killer.
This sounds like Tony is not going to be in a very stable place come May 6, 2016! I would also bet money that Ol' Thaddy Thunderbolt Ross will tell Tony that Bucky is responsible for Maria-Howard's death (Hydra's files must be somewhere, and Cap is going to be like 'Oh I know, you didn't, my bad man'). So, is Tony going along with Ross just to capture Bucky? I know, this sounds crazy (and goes against the comics), but Bucky did some s*@%!
Black Widow- We all remember (males and females) when Natasha lifted up her shirt in the Winter Soldier, to reveal..... she was shot by Bucky. I know Steve was shot also, but Widow did not grow up in Brooklyn with Mr.Barnes. If he is to blame for that United Nations explosion *cough-bs*, then the whole, wide world will be after Bucky. I do not think Black Widow will betray Ironman, nor do I think she's in the wrong, She has red in her ledger, and just like Tony feels responsible for atrocious acts, and this is her trying to redeem herself. Someone just blew up some of the world's greatest leaders, and it is better to play ball right after a tragedy (nope I am on Team Cap, so whatevs,yeah).
War Machine- Besides being besties with Tony, Rhodey has plenty of cause (besides the military orders) to want to hunt for the Red Rogsobsover(i tried). Bucky has been murdering for Hydra for a lot of years, and you can almost bank on the fact, that Bucky interfered with Rhodey's missions. Add that up with his loyalties to both Tony- and the military, then you have one peeved Colonel.
Black Panther- Black Panther is a mantle passed down generations to the King of Wakanda. If this is T'Challa in the suit in the movie, then T'Chaka (T'Challa's father) must be dead. This makes sense if he was at the United Nations meeting, because they want to make Vibranium weapons, T'Chaka was going to opposed, then boom (sets-up Black Panther). Baron Zemo (There was an Ultimate Avengers 2: Rise of the Panther animated movie with a German shape-shifting alien, I wonder if they will go that direction with Baron Zemo, instead of purple something stuck on his face? The main reason I believe this matters is in Ultimate Avengers they fought the Chitari army in New York!) will frame Bucky, and T'Challa will hunt him down, while Baron does his thing. This is another highly personal reason to go after Bucky than to do it out of a registration. This also means, that if he finds out that Bucky could be innocent, then he is more neutral than the others.
Spider-Man- Peter Parker will worship Tony Stark, and will do whatever he says for the time being. Peter is highly intelligent and he'll believe he is going after a known terrorist. Why would Spidey choose Steve Rogers side over the billionaire, genius,playboy,philanthropist? There's no other dimensional prison, villains fighting for Tony, so no reason for him to switch sides. (Until Cap's 'death', then who knows?).
Vision- You high-cheekbone android, you've had time to grow accustom to this world, and is there a little J.A.R.V.I.S left in you? He will be on the side for people, until he finds out that Bucky didn't do it, and develops a robotic crush on a certain scarlet madame. Vision might just think this is petty and fly off with Scarlet Witch. He could be the one that figures out Baron Zemo is the big bad?
I do not believe Tony is fully on board with the Accords, but because of guilt and vengeance. What happens if the big change to the Marvel Universe is not to the Avengers, but the whole world truly hating them instead? As of now, the world has been sorta tolerant, even while dropping a giant rock in the sky. Though Hank Pym in Ant-Man said they're too busy dropping cities from the sky. What happens if that's the sentiment that reigns supreme throughout the world. The Sokovia Accords are trying to supervise now, but what happens if they start hunting all the Avengers instead of to imprison,to kill. If Cap dies (fake death, merchandising, a deal with Zemo?) this will unite the factions and truly change Marvel's phase III. A house divided, is a house that cannot stand.
Captain America: Civil War in theaters May 6,2016