I finally read The Art of Captain America: The Winter Soldier from cover to cover, including reading all the storyboard and pre-viz sequences. I was completely amazed when I saw the storyboards for the fight between the Winter Soldier and Cap on the helicarrier: the shot where Bucky goes after Steve features a caption of him shouting “HAIL HYDRA!” with a feral look on his face as he moves in for the kill.
This suggests that the line was in some early version of the script, and I am so glad that somewhere along the way someone had the good sense to jettison it, because it was so tonally completely wrong and would have drastically changed the character as they developed him in the movie. It would have been jarring and bizarre to have him spout some kind of ideological slogan (one which, for me, was one of the least successful aspects of the movie), particularly after we’ve seen him trying to piece together his memories in the face of Pierce’s empty bullshit rhetoric, which he barely listens to. The only reason he gets refocused on completing his assignment is because they forcibly remove his experiences and memories, not because Pierce sways him with the power of Hydra’s super-sekrit awesome plan for world domination.
The MCU version of Bucky is, to my eyes, far more broken and dehumanized than the comics version (not that Bucky’s not broken and dehumanized in the books, because he is, deeply so), but even this version of him is not without his resources and capabilities. We see him in charge of the team of mercenaries when they attack Steve, Natasha, and Sam on the bridge and he obviously had some hand in planning that attack; we see him waiting at the end of the attack on Nick Fury, a failsafe in case the other squad didn’t accomplish their task; we see him go to Pierce’s on his own; we see him at the end, figuring out what’s happening at SHIELD and what he has to do to stop it; and then we see him in the tag at the end credits, having learned of the Captain America exhibit and going to find out about himself. It’s really tempting to infantalize him, especially after the horrific bank vault mind-wipe scene, but MCU Winter Soldier is still a pretty capable and resourceful weapon in most situations.
But he doesn’t come by this of his own free will, and he doesn’t do it because he buys into the ideology — he does it because he’s been tortured, mind-wiped, completely broken of his humanity and stripped of his own personal agency. There’s no Stockholm Syndrome absorption of his captors’ beliefs; he does what he’s told, but he’s not doing it because he follows the party line, even if he was only following it to stay alive.
It doesn’t matter if Hydra’s still just a Nazi cult or you’re viewing it through the prism of modern-day government that’s just a step away from the Big Brother-type new world order, there’s still a political (and control) agenda that the people saying Hail Hydra have bought into at some point. They clearly believe in the message. But the Winter Soldier doesn’t buy into that, he can’t — he’s a loaded gun that gets pointed in a direction and fired. He’s programmed, not motivated.
In the comics, Bucky gets out of cryofreeze for much longer times and even has something resembling a life at one point, training Red Room recruits. He’s still a weapon, though, he’s still there to do a job and complete a mission until Steve forces his memories back (not, like in the movie, through the Power of Love but with the cosmic cube’s mojo), he’s still there to represent someone’s agenda, and he seems aware of it — he knows who he works for, what he’s doing. He questions orders, goes off-mission (which doesn’t work out too well for him), and interacts with his superiors to some degree. MCU Bucky doesn’t appear to have any of that, at least from what we’ve learned so far, until Steve jars it loose and he makes the decision to save Steve. MCU Bucky is even less likely to understand or give the tiniest crap about the rhetoric and ideology of an organization like Hydra than the comics Winter Soldier is.
To buy into a belief system, you have to make a choice, and we’ve seen that Bucky in the MCU doesn’t have even the tiniest particle of free will anymore. If that horrifying chair scene does nothing else, it shows us how completely they’ve destroyed him and taken away any real knowledge of what he’s doing in the grand scheme of things. Pierce pumps up his bullshit with compliments, trying to give Bucky the carrot to get him back on mission, until he realizes that won’t work and he resorts to the stick instead. Because really, why would that crap work on him? He’s a tool, a weapon, and that’s all they’ve allowed him to be.
He’s almost completely undone by his memories of Steve, and they have to basically reboot him in order to get him to perform his mission. All this ideology, all these statements and beliefs, are meaningless to him, so having him shout “Hail Hydra!” before attacking Steve would have made him look like he had absorbed what Hydra stood for, made him more of an active participant in their plans, not a broken, dehumanized, tragic victim. He doesn’t even have enough agency to buy into Hydra’s mission or his part in it the way someone might with Stockholm Syndrome. It would have completely altered that aspect of his character to me, made him seem far less tragic than he is by the time he makes that decision to save Steve, and in doing so save himself.
I’m sure someone could make a good case why having him shout Hail Hydra would have been cool or might have made his mind-wipe even more tragic (if so, go to town!), but myself, I just can’t see it. I always find it fascinating to see what gets changed in the movie-making process as they go along, and it seems to me that someone showed very good sense in eliminating that line, keeping Bucky’s tragic storyline more consistent with what we know of how horribly destroyed he is as a person. He’s a blank slate, a weapon, a victim, not a slogan or a belief system — or even a villain with a plan.