You're missing the point, I'm not saying humans are some great force for good, they're not, but they have the capacity to make the planet less shit. In your mind what was this "initial harmony" then, 165 million years of dinosaurs, with toddler brains, walking around eating and shitting and gorging each other? That's not a good world, that's a pretty bad one, nothing harmonious about it, completely pointless.
Before say "welll erm ackchtuhally it can't be cruel because like nature doesn't have feelings" well guess what edgelord, I'm a human, with a brain, I have feelings, I can objectively understand that a zebra, with it's chest ripped open, walking around trying to push it's guts back in, scared and confused, is a bad thing. Sure, it's "just nature", and nature is disgusting.
Actually, and this is a very controversial take for some reason, I don't care if certain species go extinct. Conservationists are actually the egotistic ones, all so they can keep some dumb animals around to observe and feel good about because they're heckin' cute or whatever. Oh no this certain breed of tiger cant npc mode walk around and eat other things anymore, imagine the breadth of experience of being a tiger (none). It's all fun and cute to observe these things, but to actually be them? No thanks. You could say I'm projecting my human experience onto them, but I don't care.
>Kill or be killed is not disgusting because those who think it is die first.
I don't get what you're trying to say here, I assume you're saying, if an animal was born with a genetic defect that made them a pacifist, they would soon be deleted from the genepool? Uh, okay, much edge, not relevant if we're discussing the moral impact of humans on the planet, also, humans are the most successful animal on Earth, and all societies outlaw nondescript murder, or kill or be killed mentality, because it's objectively undesirable and bad.
Humans are just nature, extrapolated to both extremes, they can do insanely evil things (genocide, slaughtering billions of animals for meat (yet no different than your much acclaimed dog eat dog funland)), but also insanely good things (healthcare, veterinary, medicine). If you hate humans you must also then hate nature, because humans are just the end product of mother nature's tech tree.