To me that sounds like realistic, if also extremely depressing, point. I'm optimistic though. We've been successfully living in larger and larger cultures throughout history and have overcome this difficulty many times.
But I guess it is the second part that you touched on here as well. When you say take that into account.. how specifically?
Like when someone performs a racist act, how should we respond in a modern society?
One part of anti-racism is establishing principles that allow "tribes" to coexist and treat members of other tribe fairly. That's all the anti-discrimination rules, requiring commerce and employment to happen on fair principles for outsiders as well; that's all the control of violence, hate speech, threats of violence.
The other part (or is it a different direction?) is to try to form a single tribe - unification, assimilation, rallying together against an external threat, general acceptance etc. "Building a nation" if you will, reducing differences and establishing national unity, though often at the cost of some international tribalism.
If we look at the specific situations described in the original article, it seems to me that there in most of them there are no "racist acts" (violations of the first part) involved, this story (unlike many others) does not involve the "other tribe" acting horribly against the members of "his tribe" - the article focuses mainly on the fact that mr. Diallo is not treated as a "member of this tribe", and provides many illustrative examples of natural emotional pain and alienation caused by being treated as an outsider, even if outsiders are treated fairly.
And that's conceptually very different. It's reasonable to mandate fair treatment for everyone. But it's not reasonable to mandate every tribe or subtribe to accept someone (especially because usually "the tribe" is not organized enough, it's effectively a sum of individual decisions) - freedom of association is a quite fundamental thing, it's completely reasonable for someone to (for example) treat only their extended family as "their tribe"; or for someone to treat only members of their particular religion as "their tribe", shunning those familymembers who are not. It's a free individual choice. It's worth noting that if you look at any list of prohibited discrimination types, then there's a "tribe" in almost all cases. People can and will treat someone else as "not my tribe" for all kinds of reasons - political beliefs, sports team preferences, having not seen (or not liking) a particular TV show, etc, and that is their right. You can't mandate being friends with someone; it's permissible to treat Bob as an outsider just because Bob is kind of an asshole, and it's permissible to treat Bob as an outsider just because you are kind of an asshole and hate him for no good reason.
You can implement various policies to try and slowly erode factional/"tribal" differences. But you can't eliminate the tribes or determine their membership. If (for example) Montagues and Capulets hate each other, you can't mandate them to stop that hate. If someone from the Montague "tribe" wants to marry a Capulet, then you can (and should) have policies so that they can marry despite the wishes of the tribe (if they're adults, unlike Romeo&Juliet), however, if the "tribe" wants to expel them because of that and treat them forever as outsiders, that's their right which can not (and should not) be prevented.
You'd first have to define what a racist act is and who gets to decide that it is so.
We have a working system for these matters - legislative and judicial branches of government.
I'm asking a question that says in spite of not having a perfect answer when you are in a situation and you watch a friend do a racist act, what response if any do you think is appropriate? What if it's not a single act that might be considered racist but a whole string of them?
Do you think there is any kind of moral or social obligation to do anything or is ignoring it ok?
Which leads me to believe that my definition of a racist act, is different from yours.
Please provide your definition.
Also, speaking about racism particularly is something that makes very little sense historically. Racism has largely not been a problem because most societies weren't (and still aren't) multi-racial. The biggest issue has been religion and, more recently, class.
Both of these distinctions are arbitrary and should highlight that discrimination, not racism, is the problem and that is a fact of life. You will get discriminated against if you are disabled, if you have a Southern accent, if you are too short, if you are too tall, if you are too fat, if you aren't fat enough, etc. On and on forever. This is constant, it is human nature.
Btw, it is also worth saying that we largely have approaches that are effective. The only thing that history is really clear about is that constantly going over the past, seeking revenge/retribution, etc. doesn't work (many countries have gone down this route with power-sharing agreements due to religious/tribal conflict, it doesn't work). Equality means equality for all. Everyone is different. We all have to live with that. When you start from the basis that some people have an advantage/disadvantage because of their identity, the only way that ends is segregation and power-sharing agreements (usually after some period of terrorism/internal civil conflict). Everyone benefits from fairness, it isn't a race/religious/class issue.
Am I misreading you on that? If not, what kind of approaches do you think would be more appropriate?