I argue against. Lets take native Americans and irish migrants. Native Americans did not drink Alcohol before. Irish have a longer history of drinking Alcohol. Since the Europeans migrated to America the native americans also adapted drinking Alcohol. So this is an example of thousands, how cultural differences get smaller through contact.
Discussion
Yes, you can do things that decrease human differences. But this is equivalent to forcing wolves and beagles to live in the same enclosure. It is unnatural and oppressive, and can only happen when men with guns enforce it. (And it really doesn't matter if the men with guns pretend they are supporting the divine right of kings or the divine right of "the majority.") When people are left to their own devices, they tend to form kinship-based (that is, race-based) societies. And that is a natural and good thing.