It's not just Bucky. SPOILERS if you haven't seen the movie :P It's the fact that he doesn't want to be controlled by governments to do whatever they want, whenever they want. It's pretty obvious why he doesn't trust any organism to oversee them. Remember SHIELD? It's because he wants to prevent those "super soldiers" to be awaken, and he can't trust this info to the others since it comes from Bucky. And they pretty much think he's insane and they want to lock him in, again. And, yeah, because he trust Bucky. That might be selfish, but he's the only link he has with his era, he's his childhood friend... I think that there are enough reasons to the conflict. I think it even makes more sense than in the comics XD. That storyline was pretty messy imo. 

He HAD reasons to trust Bucky decades ago, not now. It is selfish to do what he does. And stupid.

There's a pretty big difference between a single government or organisation, and the fucking United Nations. If Cap is defying the singular interests of Shield, or the US government, the story works. But here he really has the audacity to think he, by himself, and every other superhero by themselves, has better judgement than the United Nations? 

I mean.......lol

And this just after Tony made Ultron, he still tells him in this movie that "the safest hands are our own"

Face it, Cap is an imbecile in this movie

These points got to me as well, fanboy wise at least. Plus I didn't like Redwing as a machine thing instead of an actual bird. :P My friends pointed out that it was silly to expect him to communicate with a real bird. I don't know what they were on about.

This is where I think they went wrong with the plot, we all knew it wouldn't be the same as the comics as well Age of Ultron wasn't and this can be the same as Civil War due to noteable absences and there are like 10 heroes.

What should have happened is remove any mention of registering or agreeing to be regulated by the UN and just have the incident with Bucky being framed. Cap goes to protect him and the others fight him for Bucky, Wanda gets annoyed at just being kept safe by Tony and Vision and leaves etc. Then mid to later mid way through the film Tony finds out the truth about Bucky how he killed his parents (doesn't matter how) and forms a team to fight cap while Cap is still investigating the truth etc. Slowly Ironman and Cap team up to take out Zemo but Ironman still hold resentment towards bucky and maybe flips near the end due to an action Zemo performs... like the code trick. Cap protects his friend etc. The Civil War should have been just about the heroes fighting instead, not any registration process with makes little sense with 10 heroes on the planet and no mutants.

Hey. Where was Nick Fury during all of this!?!

Bucky saved Captain America at the end of The Winter Soldier. He definitely has reasons to think that his old friend is still there. Who can blame a guy who can save the only friend he's had? 

I agree to some extent, but consider this:

They said that every Avengers mission would have to be approved by the UN before they could do anything. This would've made The Avengers pretty much useless. They'd use at least a week before they'd be able to respond to anything.

Imagine if some shit is going down in Russia. Do you think they'd approve to send in a de facto American team of superheroes to solve it, at least not before shit had gotten way worse than necessary?

-Double post-

The real important missions that require Avenger intervention would get them without much hassle. Nobody is going to keep them from fighting off Alien invasions, or Thanos showing up with an infinity gauntlet disintegrating people left and right.

There's no problem with them not being instantly called in for some situation like they had at the beginning of this movie. Those kinds of low threat, human engagements are what governments have their own military responses for. Sometimes it'll go better, sometimes it'll go worse, but the same is true with avengers on scene (case and point here in this movie). Then if a situation truly escalates to a level beyond their private means the Avengers can act as a last resort. I mean hell these Avengers don't/didn't even assemble for the hero's solo movie threats that truly would have benefited from another hero being there, so clearly it's not like they even feel this pressing need to be everywhere all the time. UN oversight would in no way diminish their effectiveness.

I thoroughly enjoyed the film. The story makes sense, the people actually have a clear and understandable reasons to do what they do, the villain's motivations are also understandable, the action was some of the best I've seen in a superhero film. Winter Soldier is still probably the best Captain America film, but this one came close.

Of course there are some things that requires the suspension of disbelief, such as how the villain was able to do everything he did, but those kinds of things have always been a part of the superhero film. Besides, when the film has strong characters and an interesting story to carry it small details like that are easy to overlook.

A lot of people have been comparing Civil War with BvS and honestly, it's not even close. BvS tried to do in one film what Marvel had done in over a dozen, and it showed. BvS had material for at least three different films, now its just a chaotic mess where the story never gets time to breath or build up to a proper payoff because things just need to be rushed out of the way for the next important reveal of a new character or plotline. Affleck was good, Irons was good, Gadot was good and the action was good, even if the motivations behind it rarely made sense. The rest was mediocre at best.

Civil War isn't the best MCU movie, but it's easily among the best.