I want to address the paragraph you start with “But I also think there is a basic ethnicity layer of our identity stack…”
You have to consider that the personality of the child is largely formed prior to the age of 6 years old, there is no rationality that needs to come into play. The dominant factor will be the family environment. I never attended daycare, or Kindergarten, and first attended school in 1962 as a five year and later a six year old- my birthday being in late October. By then, the parameters of my personality were largely defined within my family environment, mostly unconsciously. This has been widely confirmed by various studies. It was not the surrounding culture that formed me, it was my parents and even grandparents. I was born in 1957, so the onslaught of media was not as pronounced growing up in the late 1950s and early 1960s so the family environment was more important.
Also growing up in the Metro Detroit area there were many distinct “white” ethnic groups each with their own characteristics. You might argue that these were stereotypes but in retrospect looking at my own family background I can see how some of these ethnic qualities had an expression in my own family, and came to the forefront, not necessarily always deterministically but as tendencies.
Some other examples, I was best friends with a Greek boy my age, and spent a lot of time with his family. There was also a Hungarian couple across the street. They all had strong cultural differences from the surrounding generic American culture. I also knew Italians, Germans, Poles, Irish, Scots, French Canadian, Chaldean, Armenian, Lebanese, Jewish ( distinctive Jewish backgrounds, those from Germany and those from Eastern Europe), and then there were Americans from the South who migrated up to Detroit, and Mexicans. Western Michigan was known for the Dutch and Dutch were considered thrifty, and high quality craftsmen and builders.
Each group was distinct. All this was whitewashed over the course of some 40 years. I would say that during the 60s, and 70, up until the 80s there was a gradual melding together of these diverse groups, in part due to intermarriage but also due to socialization, and the increasing dominance of media culture. For anyone growing up in the 1960s, I think the ethnic influence was not just generic “white” but strongly influenced by nationality transmitted through family customs and norms as children growing up, and then later this was merged into more standard norms. And sure, once you went to school default norms were imposed on top of the family norms, and to succeed in a career or in the job market you would have to conform to broad norms imposed by the dominant, yes, 'white culture", but that was all after the main formation of personality prior to age five or six. And yes, I can now rationally retrospectively reflect on this process and discern or differentiate my own family customs and tendencies from the broader culture.
For someone growing up in the north, white guilt over slavery was neutralized or didn’t exist largely due to the the action of the Union fighting the Confederacy in the Civil War, and by Lincoln’s Emancipation Proclamation. When you consider that hundreds of thousands of Union soldiers died to fight against states rights and slavery, and then the long list of abolitionists like John Brown, Henry David Thoreau, etc.; a huge sacrifice was made my those in the north to combat slavery.
The majority of my ancestors came to the United States after the Civil War, and the ones who were here earlier were Quakers in Pennsylvania.
I think you have to take into consideration again that white culture isn’t monolithic and not all whites are implicated equally in perpetuating systemic racism.
We can talk about a generic “we” in reference to a society of all races and ethnic groups, but not in a way that assigns blame or judgement to this group or that group. Therefore, I also can’t be held responsible for the actions of all white people or their ancestors, that would be absurd. Likewise “my people” didn’t invent the airplane or the telephone, nor are “my people” responsible for slavery or systemic racism. I don’t even refer to my own ancestors as “my people” or “we” like in the statement: “we came over to American in 1906.” I’m an individual not some sort of tribal amalgamation.