Nature is not external to humanity and it is certainly not harmonious in the sense that everyone gets along, but ecologies function in a way where threads pulls every which way and affect every lifeform. We can prescribe that life is neutral and ecologies being "harmonious" is neutral, but we have to contend with our accountability ot each other and to the suffering of other humans and other species (read: individuals) that we can reasonably perceive as being harmed unnaturally.

"being left to itself" is too vague. Humans are a part of nature and always will be. There is no separation, therefore it cannot be left to itself. We can identify behaviors that are more or less destructive to individuals and ecosystems thriving, but we can't say nature must just be left to itself.

Environmental Ethics through Kimmerer's lens, to me, can overcome issues of human-nature dualism. She writes so beautifully in Braiding Sweetgrass and here about the spiritual grounding that kinship gives us. When we believe humans to be separate from nature or spoilers of nature, we overlook how we are nature, everything is our kin. Much of ecocentric, and especially zoocentric and biocentric ethics fall victim to a Western misanthropy. We can learn a lot from Kimmerer and others.