Biodiversity is important insofar as it facilitates human flourishing. Flowery poetry about An Idealized Past doesn't have anything to say about that. Therefore, it is uninteresting.
Because we humans seem to be the only creatures that have ever existed that have even been able to pose the question of what makes Earth "important". That level of consciousness is special and worth protecting and expanding at all costs. It's more special and magically generative than any other creature that we know to exist or previously exist.
Because Earth without us is a dead man walking. The complete extinction of all complex life on this planet is already baked into the future as the sun expands and boils the oceans in 0.5-1 billion years. It seems to me exceedingly unlikely that any other spacefaring civilization will emerge after us if we fail. Even if you think other forms of Earth life are more "important" than us, the continuation of our human civilization is the only chance this other life has at having a longer existence (on other worlds) than this baked in timeline.
That doesn't mean that I want Earth to be a hyper industrialized Forge World, but my reasoning is because that would not be a good place for humans to live.
I'm having a hard time responding in a way that meets the Hacker News guidelines. I don't want to attribute to you the implications (slavery, slaughter, environmental destruction, etc), because I have a hard time believing you actually mean that (or perhaps you thought I was only referring to the mineral aspect of the world and not the life that lives in it). I understand that you might object to slavery being implicit in your belief (because you make a special carve out for only humans mattering)- but understand that up until recently, in many cultures many people were not considered human.
The most substantive thing I can suggest is to read Hegel's master slave dialectic, and consider the upshot- that by viewing others as only being instrumental, you inhibit the development of your own consciousness.
As an aside, I also reject your claim that slaves were historically considered subhuman on factual grounds. For most of human history slaves were considered humans and subjugation was justified simply as a matter of having the might and means to do so. In a historical context, the idea of slaves as subhuman is primarily a New Philosophy developed in the Antebellum South.
I think you are correct that this is the predominant view held by humans, but it doesn't mean it is justified. It is hard to dispute it quickly without invoking something like god, which is something I am uncomfortable doing. What I can do is start with something like Descartes's meditation. Without his ability to invoke god, we are left with the paradox of the world being ultimately unknowable. Likewise if you start from the idea that there is a real world. At best, you become committed to the paradox that we are living within our own imaginations somehow embedded in our brains. From any other starting point, at some point in our reasoning we are led to a deep paradox, which seems to be a defining aspect of our consciousness. Ultimately, the world is unknowable and the best we can do is be honest, humble and do our best with what we have.
That leads me to why I reject what we both consider to be the predominant view held by humans. If we trust natural history, we can see that the mammalian anatomy has been conserved for at least 65 million years. Mammals adapted to all kinds of environments, grew large, grew small, etc, but fundamentally, the mammalian anatomy remains the same (even the whales have essentially the same anatomy as any other mammal). As long as the physics of our world remains constant, function is determined by structure. That means that the same functions that underlie our experience underlie other mammals. The only major difference with humans is that we grew out a section of our brain (the neocortex), which gives us greater ability to visualize, synthesize the input from our senses, develop speech, and interrupt other parts of our nervous system (i.e., like using meditation to quiet the mind, dampen the response from the amygdala, etc).
With that understanding, it seems deeply wrong to subjugate other consciousnesses. It seems like instead of having a "tenant owner rights" view of Earth, we should view ourselves as gardeners cultivating the planet out of a sense of beauty and love that coincides with helping ourselves and other creatures.
That is one thing I am deeply committed to. Humans exist as the most exquisite and beautiful branch of life and are the greatest care-givers on this planet. We not only give of our bodies like the other mammals to nurture, and develop groups to care for individuals, we also care so much that we care about truth, and continue to grapple with it even when it seems out of reach.
Your relating of an anthropocentric ethics to support for slavery does not make sense to me. What does the previous horrors of human slavery have to do with our relationship to non-humans?
The enormous risk we've created against there being a human future. I for one hope for a sustainable flourishing, and find any other avenue not merely uninteresting, but actively malicious & evil. Global gaian awareness is absolutely required, or you are just a primitive wild mammal.