You don't believe that people congregate based on some shared factor, race being one of them?
I grew up in Toronto, and I don't know if my perspective is anything more than just my perspective, but my group of friends consisted of all different races, and what held us together was culture. We all shared the same views, watched the same shows, used the same slang, had the same (non-existing) religion, etc. The fact that everyone was from a different background meant that we couldn't exclude people based on race, but looking at Toronto, there are distinct racial enclaves. There is a Chinese neighborhood, an Italian one, a Portuguese one, a Somali one, etc. It's human nature to band together based on commonalities, and race is a particularly popular one since it often comes with secondary commonalities like religion, dialect, traditions, etc.