I don't see any smearing of whiteness going around. That sounds like you taking things a bit too personally.
In CA:TFA, Steve was going to be sent off to a lab to be a lab rat, so it's established in MCU canon that the Americans would absolutely experiment on people. I think the story of Isaiah hits harder because he was poked and prodded by his own people, which is something they absolutely would do. Let's not forget that the Americans gave Japanese scientists immunity for their horrendous human experimentation in WWII in exchange for their data. Blaming the Nazis again in this story would just be tiresome. It's more interesting that Isaiah was imprisoned by his own government and let's face it, it's not exactly a stretch. And to tell someone they should only blame the people who did them wrong and not the whole race is rich, given how people react to terrorist attacks and Covid-19 coming out of China. Why is it that black people should be held to a higher standard than anyone else? Isaiah can blame all white people if he wants. We do it all the time.
I don't think it's Marvel's job to sing happy lullabies when people in the real world are suffering. And your complaint about not bringing people together doesn't make much sense given the last episode. Bucky and Sam are building those bridges, that's kind of the point.