What carries culture is people, not the language they speak. Do all English speaking people think the same and have no identity?

We humans are very good at both forming groups as well as self-segregation. There will never be total conformance and homogeneity. If you think certain group of people fall into that category, that's because your own lack of understanding of them rather than them being the same.

In fact, if we all spoke the same language, there will actually be more understanding and less perceived sameness or difference.