It's usually the case that large cultures can be divided into subcultures (same with ethnic groups). The question isn't whether this is the case, but whether th

It's usually the case that large cultures can be divided into subcultures (same with ethnic groups). The question isn't whether this is the case, but whether they form a larger culture with shared values and beliefs, and what those beliefs and values are. This is why the words "only" and "no shared core" appear in the question you are replying to. Saying that such generalizations cannot be made or that they only lead only to "mundane observations" is demonstrably false. The only question is whether the specific observation discussed here is correct.