But he didn't sign and should own it. It's not Zemo, or Bucky or Tony or anyone elses fault but his own in the end.
When Cap caught Bucky after Zemo activated him, why didn't Cap bring the unconscious Bucky to the UN (who didn't kill Bucky when they had him previously)?
Because he wanted to get to the bottom of what Zemo did to Bucky, and having the UN get in the way would only waste time that they did not have. By the time they brought Bucky back, God knows how much time would've transpired, besides the fact that Bucky would definitely be detained for who knows how long (if not outright killed for his earlier escape, though he was brainwashed and didn't do it of his own free will) and Cap and Falcon would've been arrested (and nobody would probably listen to them at that point anyway; once you're considered a criminal, most people don't want to hear what you have to say).
When Cap learned of the Super Soldiers, he came up with weak excuses to not contact the team. I get not contacting Ross but not letting Widow or Tony in was weak. Either would have helped Cap behind Ross's back and both later did.
Then what is the point of Widow or Tony signing the Accords if they were to just go around it immediately afterwards? That would be stupid, as it proves Cap's point that the Accords only stop them from doing what is necessary.
When Caps team was confronted at the airport, Cap could have informed Tonys side about the Super Soldiers, ask for a team up against the Super Soldiers, and offer to turn themselves in afterwards, if Cap really wanted to sign the accord. Instead, Cap didn't try to talk it out, he was just stubborn about doing his own thing.
Cap straight up told Tony about the other Super Soldiers, but Tony wasn't hearing any of it.
Cap: Hear me out, Tony. That doctor, the psychiatrist, he's behind all of this.....you're after the wrong guy."
Tony: Your judgment is askew! Your old war buddy killed innocent people yesterday...
Cap: ...and there are five more super soldiers just like him. I can't let the doctor find them first, Tony. I can't.
He tried to talk to Tony, but because of all of the distrust and events leading up to the airport scene, Tony doesn't trust Cap enough, and was feeling the heat from Ross and T'Challa enough to continue trying to take them all in, period.
Honestly, The Winter Soldier made me love Captain America and Civil War kinda made me hate him so I hate Civil War for that.
He is the same person, so I don't understand how that could be. He has to do what is right, but the Accords was a well intentioned misstep on the UN's part that this movie itself proved only got in the way. The concept of oversight on the Avengers is probably necessary, but I don't think the execution was good. If some things could be amended perhaps Cap could sign. But why would they craft this legislation without consulting those that it will be affecting directly? This is like not consulting gay rights activists before crafting Same Sex Marriage laws. And why would you sign in the hopes that they amend it later, and not the other way around? That would be foolish.
The only way that Cap is different from Winter Soldier to Civil War is that he is less trusting of government. Rightfully so, as the organization that he gave up his life to protect ended up being infiltrated by the very enemy he fought against all those years ago. His motivations are perfectly understandable and in line with his character arc, even if you don't personally agree with them. Quite frankly, if he made the choice to sign the Accords at any point in this film, it would go against his character development.
This is why the movie is a success. There are legitimate arguments to defend either side. No one is 100% in the right or wrong here. I could argue for either side. The answer is probably somewhere in the middle,