I can't speak to how races other than white were taught to think about themselves since I'm not nor ever have been nor ever likely will be anything but white. I'm sure, like most people in the US, some were taught to think of themselves as individuals and others were taught to see themselves as a collective. America being an individualistic culture, I was raised to see myself as an individual first, and I imagine the majority of people who grew up in this country have as well. In other countries, especially Communist orientated countries like China, they're likely taught to think themselves as part of a collective, hence, the majority likely do so.

Also, thinking of oneself as part of a collective isn't limited to non-whites. Plenty of white Europeans who come here, especially new immigrants, will always associate themselves as being part of their home country first. They will seek out others like them who share similar ancestry and, together, will form small collectives wherever they happen to be. So, it's not a phenomenon unique to non-whites. It's fairly common given human beings evolved to be part of and help support small groups of other, similar looking members, especially when they feel they've been discriminated against, hence the vast Irish and Italian groups that formed in many cities throughout early America when they too were demonized because of their culture.

I think the reason for the racial disharmony of today, proliferation of social media aside, is the rise in world population, specifically the population of non-whites in traditionally white countries such as the US and much of Europe. The more intelligent and rich a culture, the slower its rate of reproduction, and vice versa, hence the decline of white people. Whether or not this is deliberate, I don't know. Maybe it is, maybe it isn't. Maybe there's a vast conspiracy by the "elites" to wipe out white people from the earth for some reason (many of them being white themselves - secret sadists perhaps?), or maybe it's just a consequence of cultural success over time. I'm not a scientist or a sociologist so I couldn't tell you. Sure, it's alarming, but it's a problem so far off into the distance (hundreds, if not thousands of years, assuming no major world changes), I'm sure something worse will arise well before then and demand our attention, likely climate or technology related (AI).

"In what way is people banding together based on a common heritage ‘shallow’ & ‘dangerous’?"

If you decide to band together with a group of people strictly because of your shared heritage and nothing else, you deprive yourself of the opportunity to meet, learn from, and work with people of other ethnicities who may be smarter or more knowledgeable or more skilled than you are. It's the difference between a country like the United States, where anyone skilled enough can make it to the top of whatever field they pursue and, thus, contribute positively to the overall culture (and, sometimes, the world) through their contributions, and a place like Afghanistan, where, regardless of your skills or intelligence level, if you don't happen to be the right skin color, worship the right god, or be the correct gender, you'll be lucky to even be allowed to sweep the floors. If you build a culture based strictly on heritage rather than merit, over time, you get the difference between a bustling mega-civilization and a place where a good chunk of your population lives in shacks. The United States is a living example of what happens when you let the cream rise to the top. Or at least, it was.

I'm not against collectivism, I'm just against doing so on strictly racial grounds. If you told me you wanted to collectivize based on skill or intelligence or moral/ethical grounds, I don't think I'd have a problem with it. But to restrict yourself simply by ethnicity, in this day and age, would be cultural suicide. There's plenty of dumb, ignorant white people I would never want to group myself alongside, and plenty of brilliant non-whites I would gladly join with, if push came to shove. And vice versa. Nothing to do with any prevailing narrative, it's just an observable fact of life: if you want to be part of a successful group, whether it be social or professional, in business or global, you should strive to surround yourself with intelligent, skilled individuals you can work well with, regardless of their ethnic backgrounds.

What constitutes as "white" for you, exactly? How many years of European lineage must one have before he's considered truly white? Is it 2000 years? 5000? How many generations back must it go? Would one non-white ancestor thrown into the mix at any point mess things up, or are a few here and there allowed? What is considered pure?