Considering that Kozumi "transcended" humanity I don't think he considers himself human anymore, therefore whatever happens to human is of no concern to him. He evolved from human, like human evolved from apes, and like human who do not consider apes our kind, he wouldn't consider human as his kinds.
I know that is how he sees that... but that isn't the truth.
Apes do not have the same capacity for thought as humans, they are more capable than some animals, but they still don't have human "higher thought".
Kozumi certainly can understand certain concepts of reality better than most humans... but he is still human, he simply is a "strong exemplar", and that... is his folly.
He distanced himself from his own race because he became arrogant and unsympathetic, he decided to deny the "higher thought" of others simply because of his own circumstances.
He "recognises" certain individuals simply because of special traits, but he became apathetic to the smallest of "seeds".
I know why reality itself conspires against him... because as sad as it is, as terrible as it is... the death of the kame is simply part of the natural cycle, people evolved, and their dependency on the kami diminished, sure... this lowers the wonders of the world, but it brings out others, it is life at work.
What he is doing, however... does it seem natural in any way to you? Mind... altering reality beyond its designs is something I appreciate in a narrative... but not at this cost, he isn't even killing them... he is depriving them of the most fundamental aspect of being a person, he is taking away from others exactly what allows him to be what he is.