What is the root cause of racism?
A very complex question, with not a single cause but many levels of overlapping cause.
Mostly it comes back to people existing in competitive rather than cooperative environments (at various levels), and thus back to evolutionary selection pressures at both neural and cultural levels over deep evolutionary time spans.
If people are in competitive environments, then knowing who you can trust is important. At many different levels of biology and culture that tends to select patterns that make us prefer others like ourselves, and be wary of those who are different. Racism is one obvious form of this, there are many other sorts of discrimination based upon behavioural or belief differences. Some aspects of those patterns are directly embedded in the neurophysiology of our brains, and other aspects are in patterns that we learn both implicitly and explicitly through culture.
All such patterns can be overridden by conscious choice, and that is most easy to do in a context of relative abundance.
One way to achieve a context of relative abundance is to train oneself to desire very little, another way is to automate the production of things desired, and in reality most real people have some mix of both sets of strategies in different contexts.
Market based systems are fundamentally based in scarcity and require more active choice on the part of individuals to overcome tendencies towards racism.
Many cultural systems tend to have strongly embedded racist tendencies in the simpler forms – fundamentalism of any sort, religious or any other cultural form.
The more competitive the environment, the smaller the set of “other people” we tend to identify as being “like us”.
The math and logic is quite simple from there.
Creating systems that deliver reasonable abundance to everyone creates an environment where racism can more easily be eradicated, and doesn’t immediately eradicate racism; that requires active work at the individual level to identify and change tendencies present from whatever source. Part of that process is creating expectations of reasonableness that are technically achievable.
It has been a deep shock to me over the last 6 years how many people would rather die than change their diet. So some aspects of racism are likely to take quite some time to remove entirely.