The way the people who promote “natural values” talk about “natural” is usually about “try to live like a tree (1)” or something similar of the sort. “Natural fallacy” is a thing, so there’s not much to discuss about this. But some might understand “natural” as “without human interference (2)”; and I think this is the definiton of “natural” that you used in the first 4 paragraphs. I attempt to refute this idea by asking a question you might find familiar: “How much is nature, how much is nurture?” Perhaps, it is natural for human to be altruistic. Perhaps, it could be an evolutionary advantage, for us to sympathize and help and interfere, as that is how humanity have banded together and build our civilization for the last thousands of years.
About the last part, yeah, I share your contempt toward Capitalism, for the same reasons and else. But I think nature’s brutality can be seen from a purer point of view, that it is less about optimization and more about adaptation. And also, a huge missing part that is too lengthy to talk about, is the relationship between intelligence and evolution.