If they had agreed to simply arrest him, take him into custody, then everything could have been avoided.
Well yes and no. "They" was Ross and the government. Tony had nothing to do with that. So no amount of talking between Tony and Steve could have prevented that. And even besides that, the ultimate trigger that broke things down was Steve discovering that Tony was
which is a separate issue from Bucky.
So, again, it's an argument in favor of Captain America's viewpoint. In fact, as pointed out New York was almost nuked by the "world council" and SHIELD was taken over by Hydra, so neither of those were the fault of the Avengers, and in fact, they saved (potentially) millions of lives in those situations. It was the "powers that be" that was the problem there.
But, really, all that shows is that Steve Rogers is not a very good negotiator that none of that was ever mentioned.
As I mentioned, I think both sides did not present the strongest possible argument for their sides, but I think the germ of both positions is there (and real people don't always come up with the best arguments on the spot in real life either). I think the strongest argument for both sides comes down to this:
Team Cap: The Avengers are here to protect people, not just from foreign or alien threats, but all threats, and that has often included the people in power. You say we are the powerful people that the world needs to be protected from, but the biggest threats have come from people possessing more mundane but no less dangerous power. SHIELD experimenting with the Tesseract in secret. The World Council ordering a nuclear strike on US soil out of fear. HYDRA infiltrating the government to build flying assassination engines. The Avengers exists specifically *because* we now live in a world where some threats can't be resolved by normal means. Signing the Accords is basically saying we'll play along in the very system we're supposed to be a check against. What if the next big threat is something the Sokovia committee misjudges? What if it is something they miss entirely? What if it is
something they are actively trying to do themselves?Team Iron Man: Governments make mistakes, and sometimes horrible ones, but they are far more accountable to the people than the Avengers are. We can't protect people if they don't trust us and whether it is true or not is irrelevant: the SHIELD documents caused the people to distrust us, Sokovia caused people to distrust us, Ghana caused people to distrust us. If the governments of the world turn against us, we won't just be fighting the next Ultron or Loki we'll be fighting the governments of the world as well. What happens if the next big threat is something we miss *because* no one trusts us enough to tell us? What if the governments of the world stop trying to regulate us and start straight up prosecuting us for war crimes.
And maybe you think you can do better, but do you think *everyone* can do better? What about every other super powered being that wants to play Avengers. How can you say they need oversight if you're unwilling to accept it for yourself? Do you want people to follow your example of defying the government and just doing whatever they want?