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
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.
The united states for example, current situation acknowledged, saw a meteoric rise even with, perhaps even because of a rich cultural tapestry that could be in no way described as coherent. Sure there are large blocs of cultural identity across multiple regions, but that's about it, and even then that's been on the decline for some time.
Some German states also have multiple official languages, that by itself is not the example I made.
A society needs a common ground the foundation. If a democracy or equal rights for everyone is desirable and other things.