People in the 30s were afraid of anyone who looked slightly different to them because they might kill humans and take their jobs. And then some fucks actually killed humans and took their jobs out of fear said humans might kill humans and take their jobs.
Its hard to say, comic Cap could probably throw his proto-vibranium shield and fuck MCU Ultron's whole world.
But the point of Captain America is not that this move would harm Ultron. The point is Cap would choke a robot to hold it off for even one more second as it tried to harm others, and he did just that. And that's true no matter what version of Captain America we are talking about, except maybe not Captain Hydra while he is brainwashed.