Suffering exists only because it was good for our genes. Conditionally-activated negative emotions were fitness-enhancing in the ancestral environmen… - David Pearce

Human intuitions are systematically biased. Evolutionary psychology explains how our moral intuitions and the rationalisations they spawn have been shaped by millennia of natural selection to maximise the inclusive fitness of our genes, not to track the welfare of other sentient beings impartially conceived. Many human cultures have found nothing intuitively wrong with aggressive warfare, slavery, wife-beating, infanticide or female genital mutilation. Ultimately, folk morality is a doomed enterprise as hopeless as folk physics. A mature posthuman ethics, I'd argue, must be committed to the well-being of all sentient life; and mature posthuman technology offers the means to deliver that commitment.

[O]ne might naively suppose that a negative utilitarian would welcome human extinction. But only (trans)humans - or our potential superintelligent successors - are technically capable of phasing out the cruelties of the rest of the living world on Earth. And only (trans)humans - or rather our potential superintelligent successors - are technically capable of assuming stewardship of our entire Hubble volume.

To be sure, risks abound; but no one is proposing compassionate stewardship of ecosystems by philosophers. Humans are capable of choosing our own future pain-sensitivity too; but any species-wide genomic shift in human pain tolerance will depend on the willingness of prospective parents to use preimplantation genetic screening.