I've known non-religious people who identified as Jewish ethnically, and people who converted to the religion from other backgrounds. It can certainly be either/both.
I look at the whole racism thing this way:
1. In groups and Out groups. Maybe it's our basic monkey brains, our primitive wiring, but it's natural and easy to feel most comfortable around the kind of people you grew up with, and the less diversity in your closest contacts growing up, the more that is probably going to be the case. There is a tendency to view "outsiders" as threatening, as an ant would an invader from another colony, as a primitive human would someone from another tribe. Hell, I've known "racist" dogs, who only liked and trusted black people because they'd only ever lived with a black family. Dogs were programmed to adapt to human needs, and to a degree, that tribalism is easily part of their wiring, too sometimes. (EDIT: It's no excuse, it's a starting point in what I am saying.)
2. The "Powers that Be" in my opinion (leaders of government mostly, and those affiliated and invested in keeping people under control) prefer to keep people divided, distrustful of their neighbors. There was an article about why poor white people trusted Trump, or have trusted conservative politics...and much of it is encouragement of racism. Racist ideologies have been used to push any number of agendas, including the prohibition of marijuana which was mostly to protect the business interests of Hearst and DuPont. But hey. Those scary Mexicans and black jazz musicians gonna lure your white wimmin with the devil's weed! Racism was a tool for the powerful to manipulate the masses, through American history, certainly. To say nothing of other continents and nations, such as in South Africa and Australia. Seems the Brits were very keen on using it to justify their colonial expansions, and it's just been a mess ongoing.
3. In consideration of that, I ask readers to contemplate the mental images: A group of white people...A group of black people...A group of Asians...A group of Hispanic people... Etc. Imagine in your mind, what kind of income range and type of work they do, what kind of housing they live in, if they are in a segregated group (as is still too common in the US.) Yes, there are poor whites who live just as poor as the poor of other groups, that is true. But if you can point at one group with more of a representation in the middle, upper middle, and especially the highest socioeconomic classes, they will be overwhelmingly white in that pie chart. And THAT is where talk of "privilege" comes into play. Because the ones with the most power, are still mostly white...and also...male.
It is something that even my not-a-feminist self wants men to understand, when we see photos of committees and groups crafting policy for our health care and wellbeing, and it's a room full of men, that makes my blood boil, and I know many women feel the same. Hell, how very far behind the curve, is SCIENCE for the love of fucking god, in even understanding female anatomy, compared to male??? Why are people still arguing over the Skene's gland and why did my health class have accurate illustrations of the structures and functions of a guy's business, but I'm only just now learning about how the internal clitoris is structured in the last few years?? This should be NO mystery! I still get to read about how female pleasure in sex serves no actual purpose. Great. Pen me up and call me Betsy, since evidently I'm livestock, and my human experience means nothing. Ya bastards.
It's this thing that I keep seeing, and seeing, and seeing, where the mansplainin' of whatever evolutionary or breeding strategy is served by some behavior is used as justification to treat other people badly. OK, so maybe something about our nature can be used as a starting point, but if we stop there as though it's just the right and proper way things are...? Personally I think that as The Thinking Animals, we CAN do better, so we have an OBLIGATION to do better, and I'm sick of hearing people scrambling for excuses as to why they should not HAVE to do better.
(Again, this is a more enlightened forum. The net is dark and full of assholes.)
EDIT: I jump back and forth between race and sex because of the concept of privilege. This is a pretty good illustration of my own, actually, that I more easily speak to my own experience, which is that of a white female. So yeah, I've felt it when I've been among a mostly black or Hispanic group as the only white person, that "you are not one of us" discomfort, and near-hostility. And confronted with the idea that I have racial privilege, the question is...what do I personally do about that? I don't honestly know, other than to care, be compassionate, support policies and leaders who seem interested in equality, and be generally pissed off that there are children born into racial groups where the odds that they'll experience upward economic mobility and a good standard of living, aren't so great. I've lived in poverty exactly long enough to know that it SUCKS.
The book in question was probably
The Denial of Death, a 1973 work of psychology and philosophy by Ernest Becker.
https://en.wikipedia.org/wiki/The_Denial_of_Death
It's a book I'd like to read, but haven't gotten to yet. You hear about it all the time in "intellectual" circles.
I've spent a lot of my time lately reading about climate change -- for a series of articles I'm planning to write.
Since I think our climate crisis potentially threatens the continuation of human existence (and that of most species on this planet), I've been taking my own deep dive into questions of meaning, purpose and mortality (individual and collective).
It was, and I want to read it, too.