Except they didn't leave him to rot in prison, he and Clint simply took a deal later to be with their families.
Last time I checked, Scott is actually a fully grown man, powers aside. They asked him for help, he made the decision to help. He was warned what might happen, and went through with it anyways
It's a good movie on it's own but it's very bad if you compare it to the comic version.
Err, it did drive the plot forward.
That fight was crossing the Rubicon for the Avengers. By the end of it, only 3 Avengers weren't outlaws/wanted fugitives (I'm not counting Spidey and Panther), destroying the team. Cap and Tony both lost all their backup and Rhodes was nearly killed, escalating the tensions between Stark and Cap. And hell, destroying the Avengers was a major trigger for Stark, so there's that on top of his best friend nearly dying
What I hated most about Civil War though, is that Russos made Cap a selfish ahole. I get its their attempt to make him relatable, but its Captain America. He should be a paragon. Not someone who screws over everyone else because
"He was my friend"
And seeing the fallout of S.H.I.E.L.D. going down, especially due to them releasing top secret files makes me hate him even more.