By far my greatest dread in life […] is that (some variant of) the Everett interpretation of Quantum Mechanics is true. - David Pearce

[N]othing is too terrible to be true if it is consistent with the laws of nature [...].

The Hedonistic Imperative outlines how genetic engineering and nanotechnology will abolish suffering in all sentient life.
This project is ambitious but technically feasible. It is also instrumentally rational and ethically mandatory. The metabolic pathways of pain and malaise evolved only because they once served the fitness of our genes. They will be replaced by a different sort of neural architecture. States of sublime well-being are destined to become the genetically pre-programmed norm of mental health. The world's last aversive experience will be a precisely dateable event.
Two hundred years ago, powerful synthetic pain-killers and surgical anesthetics were unknown. The notion that physical pain could be banished from most people's lives would have seemed absurd. Today most of us in the technically advanced nations take its routine absence for granted. The prospect that what we describe as psychological pain, too, could ever be banished is equally counter-intuitive. The feasibility of its abolition turns its deliberate retention into an issue of social policy and ethical choice.

Suppose we encounter an advanced civilization that has engineered a happy biosphere. Population sizes are controlled by cross-species immunocontraception. Free-living herbivores lead idyllic lives in their wildlife parks. Should we urge the reintroduction of starvation, asphyxiation, disemboweling and being eaten alive by predators? Is their regime of compassionate stewardship of the biosphere best abandoned in favour of "re-wilding"? I suspect the advanced civilization would regard human pleas to restore the old Darwinian regime of "Nature, red in tooth and claw" as callous if not borderline sociopathic.