Brainwashing or not, Bucky is a domestic terrorist and should be treated as such.

I think the difference lies between real life "Brainwashing" and movie "Brainwashing". In the movie it was more of a mind control that also erased the persons agency. Real life "Brainwashing" is more akin to "convincing". So in the movie it really isn't Bucky's fault. It's Hydra and The Winter Soldier who are really to blame.

Removing the politics (where I agree with Tony Stark and the Sokovia Records), friendship doesn't trump a guy whose actions in two movies have essentially caused three 9/11's.

From what I could tell, Cap (and Bucky for that matter) was less trying to avoid 'responsibility' for something, and more trying to A) get a trial (vs being murdered) and B) expose the actual terrorist.

Cap also lied to Tony about how his father died just so Tony would try to go easier on the both of them when shit hits the fan.

I don't think he knew the full story until Tony did, and idk if you can say that was his logic at any rate.

You can argue the Avengers do the right thing even when the governments don't agree; you can't agree that a brainwashed psychopathic mass-murderer isn't a villain.

Again, this is 'movie' brainwashing which actually does make him not a villain. If I physically grab your arm, put a gun in your hand, put my hand over yours and force you to pull the trigger, killing an innocent person- are you responsible? Does it not matter if I literally forced you to do it? What if instead I put electrodes into your brain? I don't "physically" force you, yet you are literally powerless to stop it. What if it was a movie trope and we are characters in a movie? At what point does it become the victims 'fault'?

How he's treated as a regular dude by Steve, Sam and is basically not even questioned by Ant-Man and Black Widow is beyond me.

I think Sam and Ant-Man just trusted that Cap knew what he was doing. How long do you have to be the literal symbol of 'truth, justice, and 'The American Way' before you are able to get the benefit of the doubt from your friends? Black Widow was on the other 'side' for most of the movie.

This is in stark contrast to Captain America's moral fiber as well: Captain America is a war-hound. He always tries to "punch his way out" of situations

Was he given a choice? No one was even listening to his side of it and had literal German Murder Squads coming to kill his best friend (who was also a war hero) he knew to be innocent.

and at best shows mild sympathy to the Wakandians who were casualties of their fight with Crossbones.

How can you say that? He was in Wakanda trying to protect the people from Crossbones. By putting his very life on the line. What happened wasn't even under his control (He didn't ask Scarlet Witch to do what she did) and you could tell he was not happy at the outcome. If you risked your life to save people and were instead blamed for casualties that you literally had no way to prevent you might take exception to that characterization yourself.

Why would he still love Bucky when he is a.) a criminal

I saw my dad Jaywalk one time. I still loved him.

b.) a former shell of himself?

So, you would abandon a friend because they had been the victim of a war crime and had severe psychological damage as a result?

At best, he should have agreed to be an informant for the government, explained his situation and helped the proper authorities find and identify Zemo.

If Cap hadn't helped him, Bucky would have been assassinated. If Bucky would have held up his hands and screamed "I surrender" he would have still been dead. They were coming there specifically to kill him, not capture him.