Also, I want to point out that the moral issues are nowhere near as clear-cut as you (and Kant) seem to think. Even if you axiomatically assert that people have terminal value, you still need to explain why people have that value, whereas trees (for example) do not. And also clarify the boundaries of that protected class "people". (Does it include fetuses, conceptuses, persons cryonically frozen, HeLa cultures, etc.?)

What if I were to ask the same question about why society should be valued?

Is it possible to answer these questions without once veering into the realm of instrumental values?

If you keep trying to justify values instrumentally, you'll wind up in an infinite regress.