Unpopular (?) opinion about the serum…
I don’t think the serum necessarily increases any kind of personality traits within a person when they take it. What the serum is representative of is power - not just physical, but power in general. And when people gain power, they don’t necessarily change as a person, but it reveals things about them.
When Steve Rogers took the serum, he didn’t become a better person. That little kind-hearted spitfire of a man with brittle bones and shitty lungs was no less brave than the muscular hunk he became after the serum. What changed was that the serum gave him power, and because of that people could finally see his bravery and goodness. Because people don’t look twice at disabled people, but they’ll pay attention to a military poster boy built like a brick house.
When John Walker took the serum, he didn’t become a more violent, angry man. It just allowed him to express his violence and anger in a more catastrophic way. Because that’s what power allows people to do. When you have more power, your good deeds are more visible, more impactful - and so are your misdeeds.
And I think it’s really interesting, considering the title and theme of the episode, that almost as soon as John took the serum - as soon as he gained this new power - everyone saw his darker side. Everyone realises that John Walker wasn’t such a great guy all along.
GOD I ADORE THIS POST AND AGREE WITH IT SO MUCH!
The serum really is a metaphor for power, while in the MCU is just makes you physically stronger. And we all know how humans handle power.. catastrophically. Just look at what we do to animals just because we consider ourselves the superior race (cough Nazis cough)
And yes, Steve was no less brave when he was that boy in the alley (the person that Bucky chose to follow. He was never with the stars and stripes thing, just his bestie who he knew was amazing and brave and kind and good). But as OP correctly said, being the military's poster boy brought Steve to attention.
BUT what people loved about him (and I'm sure many never even realised it) was that he was a man of GOOD morals and not just a military puppet.