Even before his transformation into the star-spangled Marvel Cinematic Universe, Steve has continually chosen to do the right thing, even at the expense of his own heroic identity — breaking the rules just enough to achieve his goals and defend the innocent.
In Steve's introduction in Captain America: The First Avenger, it is clear that Dr. Erskine was drawn to his defiance before selecting him as a candidate for receiving the Super Soldier Serum. First meeting him as Steve attempts to the army after illegally misidentifying himself, Erskine is seemingly taken in by Rogers' assertion that he doesn't "want to kill anyone" and he doesn't "like bullies." Even with personal risk and the threat of legal action, Steve still attempts to enlist because he knows it is the right thing to do. During his basic training at the Strategic Scientific Reserve, Steve's flexibility with the rules helps him capture a flag not by climbing but by knocking over the flagpole, demonstrating the character's tendency to circumvent convention in order to actually accomplish something — a trait that is explored later in the series.
Steve's signature quote, "I can do this all day," is an assertion of his defiance. Consistently written as a man unwilling to settle for a role given to him — especially when he views that role as at odds with his mission centered around protecting others — Steve stands up to a variety of "bullies," regardless of who they are. His refusal to fall in line even with the intentions of the United States government in Captain America: The First Avenger is significant. After shirking his "duty" of selling bonds with propaganda and performance centered around him, Steve goes off on his own to rescue Bucky and the other soldiers captured by HYDRA. The move reflects the character's defiant shedding of American symbolism and his more docile role in the war effort in order to put his extraordinary abilities to the use that Erskine intended them.
In Captain America: Winter Soldier, Steve's defiance towards the government grows further as he realizes that S.H.I.E.L.D. (secretly overtaken by HYDRA operatives) is not nearly as noble as he originally thought. Again allowing his own moral code to supersede the procedures put in place by governmental structures, it is notable that Captain America is the one who calls for the agency's dissolution with the intention of building something separate, which eventually takes the form of the newly-recruited Avengers team. But when his Avengers are questioned in Captain America: Civil War, Steve still defiantly stands up for his team (and himself) when under fire by the U.S. government, remarking, "The safest hands are still our own." The film ends with Captain Rogers' completely abandons his role as America's poster boy and sheds all patriotic imagery from his uniform, even at the expense of the government and media painting him as less heroic.
Dr. Erskin's advocation of Steve Rogers as the recipient of the Super Soldier Serum is not all that surprising, all things considered. Erskin, who escaped with the rise of the Nazi Party and was pursed by the Red Skull, would know the dangers of blindly following orders all too well. It is clear that Steve was selected, not because he played by the rules, but because he demonstrated a willingness to ask himself if his actions were fundamentally virtuous, even when at odds with the government.
While Steve Rogers' tenure as Captain America may be over, it is notable that he chose Sam Wilson — who has also assumed great personal risk to rise up against oppressive systems — as his successor. Kindred spirits since Captain America: Winter Soldier, both Steve and Sam look beyond the current status quo and continually aim for something better, not because they lack patriotism, but because they refuse to rest until their country lives up to its promised ideals. Erskine would be happy to know his legacy lives on.
