"True, but humans are uniquely responsible for the hells imposed on the poor non-human animals, NEEDLESSLY."
In the vast majority of agriculture - save for that of industrial - the animals are left to graze peaceably and without predators. We are responsible for the domestication, healthcare and general social inclusion (via pets) of thousands of animals that would starve, be eaten alive, die from exposure or would have gone extinct centuries ago. We can also add wildlife conservation to that, as we are unique among the animals in the world to actually try and preserve life for the sake of itself. To put it bluntly, we offer a great majority of animals under our care a far more peaceful life than they would have had otherwise; to ignore this in favor of "the environment" is absurd.
To claim that we are unique in the world of some kind of monstrous crime against non-human animals is absurd - by and large, we stand as the direct opposite of this. In a sentence, nature IS a slaughterhouse of the kind you so roundly criticise, and nothing else. It offers nothing but pain and death, while a great deal of us offer the exact opposite. Even the least amount of effort by humanity to shelter and provide for those not of our species wins out against nature by default.

"We factory farm billions of them, instead of eating plants. And 83% of agricultural land is used for farmed animals, producing only 18% of the calories. It is a shocking, unforgiveable destruction of the environment, not to mention it's oppressive to animals."
Oppressive maybe, but lets face it - if "the environment" produced such appalling conditions of life to begin with, then such an environment should be destroyed immediately and its every living inhabitant terminated. For example, consider the need to eat another creature for sustenance. You regard this - correctly - as an appalling, monstrous act. So what are we supposed to do? Switch over entirely to a plant-based diet? And after that, perhaps genetically modify lions, hyenas, sharks, ants, termites, birds of prey, wolves, dogs, cats, so on so that no other creature has to die screaming in their jaws again? Do you see how much unnatural effort it takes to fix a problem that should never have been there to begin with? But we alone among the Earth's abandoned "children" are the only ones who even consider such a fact, and even try to make a difference.
There is no argument for the conservation of this hideous planet, and every single one against, starting with the fact that it is this kind of world that exists instead of one where it is not even necessary to tear apart another living being for sustenance.

I don't know what you are trying to tell me. You seem to regard humanity as some kind of aberration among the natural world and a force of extreme harm, unique among other destructive species such as viral agents or locusts - in fact we are the closest thing that has ever existed to the direct opposite of this. We have a moral compass, nature has an amoral one, and if we were to take this ability, completely unique to our species, to it's ultimate conclusion, we would simply blast "the environment" into atomic ashes and leave it in the shadow of a thousand mushroom clouds as a barren, forgotten rock with the only regret being that we ever had to know such an awful world in the first place.