Cultural preservation is for museums when it can no longer be organically sustained. Coherence is as non-sensical as trying to preserve eye and skin color. Culture is mutable and always will be. You might as well try to stop the tide
Preservation not in the stricter sense, but meant as "reasonable slowly moving culture" as it implies stability. You also need coherence to some degree to maintain a functional society. As an hypothetical extreme example imagine one half of the population not even understanding the language of the other half, such a society would break apart real quick.
Culture is as mutable as borders of nations. Culture and nations are often seen as synonymous, to the point where one often get defined by the other.
Valuing a nations culture, values in society, borders, and maintain coherence within society are not far right idea. All political platforms strive more or less for those things, through they do differ on what values they want to focus on and deploy different strategies.