Diversity worth having presupposes a principle of unity that controls the diversity. Diversity must be checked and balanced by the competing value of unity, a value with an equal claim on our respect.
Example. One language only in the public sphere makes possible many voices to be heard and understood by all. To communicate our differences we need a common language.
Talking with one another is preferable to shooting at each other. Polyglot 'cultures' are more conducive to shooting than to talking.