Why do not you let everyone speak the language he wants, choose the flag he wants, the laws he wants, the food he wants, having his sons of the eyes' colour he wants ? I think the problem is not in the diversity, but in imposing something to another person. If someone wants to marry a guy from a different skin colour, evviva !, that's good, and if someone doesn't want let him do what he wants. To unite humanity suffices respect for other decisions