I suppose I could step in as a sort of opposition here. I'm very concerned with the death of indigenous cultures, due to the influx of new people, and excessive cultural blending. Through trial and error, over thousands of years, cultural groups all over the world have made useful discoveries about the physical world, about government and society, about medicine, diet, and healthy ways of living, which can be beneficial in ways the rest of the world may not recognize or understand. And when cultures blend and mix without maintaining their distinctness, that knowledge can be lost permanently. And for that knowledge to be forever lost is a terrible thing for everyone.
The United States are often seen as the pinnacle of cultural blending. We cherry-pick practices from all sorts of peoples and traditions. However, many to most US Americans don't keep in touch with their cultural roots, and the knowledge and practices that came with them. You could argue that the dietary problems in the US are tied to the loss of traditional diets and healthy eating practices in most US families. Traditional cultures have perfected balanced diets and meals over thousands of years... and without these deep-rooted food traditions (and an abundance of unhealthy food options), many people in the US end up eating very unhealthy things.
As a different example, perhaps you are familiar with the Marshal Islands in the Pacific, and how their indigenous populations were shuffled around by the US in order to perform Nuclear Testing. Historically, the Marshallese were able to navigate the ocean from island to island, supporting an extensive trade network throughout the Pacific... and they did this without maps, compasses, or astronomical tools, using a complex series of charts that marked the ocean's currents. Due to their populations being shuffled, and then absorbed into other cultures in the wake of the Nuclear Tests, most of their culture was lost, including their deep and extensive knowledge of the Pacific currents and long-term weather patterns. Their charts appear to be incredibly nuanced and detailed, but surviving Marshallese people and modern researchers are unable to read them. Their knowledge of currents and weather patterns would be invaluable to climate scientists and oceanographers today, but their traditions were destroyed by emigration and excessive cultural assimilation.
Technologies for farming, animal handling methods, dietary practices, medicines, languages, histories, and storytelling traditions, even political systems... all these things can be lost if we don't shepherd our cultural heritage. And these losses are felt by the whole world. That said, do you think it's important to preserve these traditions? And how can we practically do this, in a world of cultural assimilation?