At first I disagreed with the author that we cannot have a multi-cultural society. And then I thought some more about what we get when multiple cultures make up a system (e.g. society). We evolve the system through the synthesis of the multiple cultures.
We all are parts of many cultures - self, family, community, company, nation. The systems to which we belong have norms, values, behaviors that identify them. We can choose to integrate or not into different systems; we may feel that we assimilate more or less into them depending on the time and energy we choose to commit.
I believe as we open our minds to crossing cultures, we evolve society to reconcile differences and see ways to synthesize those into a new whole. This is taking a higher conscious perspective, believing we are all connected in truth and we create separation.
As we open ourselves to understanding self and others, we start to reconcile paradoxes of cultural difference we encounter – how this is true AND this is true. As we do, our consciousness expands to hold both. We evolve; the systems evolve.