The conflict between individuality and cultural consistency is practically as old as civilization itself. Most ideologies throughout history included ad hoc, unprincipled, case-by-case solutions to those problems.
Why do you think that multi-culturalism is more inconsistent and unprincipled than any other historical solution to the individuality / group identity problem?
The problem is not that it is inconsistent and unprincipled, but that it is inconsistent and principled.
The problem is not that it is inconsistent and unprincipled, but that it is inconsistent and principled.
But it isn’t inconsistent.