I like to focus on people, and the effect the loss of their language can have on them. Indigenous persons are often viewed as museum entities, as things objectified, that don't really coexist with us in our Western world. But they do. You often see this argument in discussions about African American English. But this is a total fallacy.
All languages can express abstract ideas, science, and art equally, though maybe differently.
Every language had to adapt to new realities. When a language is lost, people and peoples are deprived of one of the major assets of cultural identity. Among the basic rights of humans is the right to their own culture, and to their own language. Let's defend that right.