Being forced to endure torture rather than dreamless sleep, or an otherwise neutral state, would be a tragedy of a fundamentally different kind than being forced to “endure” a neutral state instead of a state of maximal bliss.

... when we take into account what we know about happiness and suffering in psychological and neuroscientific terms, we find reasons to doubt that (to use Popper’s phrase) we can treat degrees of pain as “negative degrees of pleasure”, and to doubt that pleasure can ethically “cancel out” pain — any more than putting people far above a water surface can cancel out or outweigh the bad of putting people far below it.

I am not suggesting we should be skeptical of the notion that life can get a lot better. Yet this should not be confused with the question of whether any better state we can reasonably expect to bring about — such as a much happier state — can ever morally outweigh all the suffering its creation would entail, including the (risk of) extreme suffering.

... if suffering warrants special moral concern, the truth is that we should never forget about its existence. For even if we had abolished suffering throughout the living world, there would still be a risk that it might reemerge, and this risk would always be worth reducing.