"What's the worst that can happen?" goes the optimistic saying. It's probably a bad question to ask anyone with a creative imagination. Let's consider the problem on an individual level: it's not really the worst that can happen, but would nonetheless be fairly bad, if you were horribly tortured for a number of years. This is one of the worse things that can realistically happen to one person in today's world.
What's the least bad, bad thing that can happen? Well, suppose a dust speck floated into your eye and irritated it just a little, for a fraction of a second, barely enough to make you notice before you blink and wipe away the dust speck.
For our next ingredient, we need a large number. Let's use 3^^^3, written in Knuth's up-arrow notation:
- 3^3 = 27.
- 3^^3 = (3^(3^3)) = 3^27 = 7625597484987.
- 3^^^3 = (3^^(3^^3)) = 3^^7625597484987 = (3^(3^(3^(... 7625597484987 times ...)))).
3^^^3 is an exponential tower of 3s which is 7,625,597,484,987 layers tall. You start with 1; raise 3 to the power of 1 to get 3; raise 3 to the power of 3 to get 27; raise 3 to the power of 27 to get 7625597484987; raise 3 to the power of 7625597484987 to get a number much larger than the number of atoms in the universe, but which could still be written down in base 10, on 100 square kilometers of paper; then raise 3 to that power; and continue until you've exponentiated 7625597484987 times. That's 3^^^3. It's the smallest simple inconceivably huge number I know.
Now here's the moral dilemma. If neither event is going to happen to you personally, but you still had to choose one or the other:
Would you prefer that one person be horribly tortured for fifty years without hope or rest, or that 3^^^3 people get dust specks in their eyes?
I think the answer is obvious. How about you?
I have mixed feelings on this question. On the one hand, I agree that scope insensitivity should be avoided, and utility should count linearly over organisms. But at the same time, I'm not really sure the dust specks are even ... bad. If I could press a button to eliminate dust specks from the world, then (ignoring instrumental considerations, which would obviously dominate) I'm not sure whether I would bother.
Maybe I'm not imagining the dust specks as being painful, whereas Eliezer had in mind more of a splinter that is slightly painful. Or we can imagine other annoying experiences like spilling your coffee or sitting on a cold toilet seat. Here again, I'm not sure if these experiences are even bad. They build character, and maybe they have a place even in paradise.
There are many experiences that are actually bad, like severe depression, severe anxiety, breaking your leg, pain during a hospital operation, etc. These do not belong in paradise.
If you imagine yourself signing up for 3^^^3 dust specks, that might fill you with despair, but in that case, your negative experience is more than a dust speck -- you're also imagining the drudgery of sitting through 3^^^3 of them. Just the dust specks by themselves may not be bad, if only one is experienced by any given individual, and no dust speck triggers more intense negative reactions.
There's nothing important about the dust-specks here; they were chosen as a concrete illustration of the smallest unit of disutility. If thinking about dust specks in particular doesn't work for you (you're not alone in this), I recommend picking a different illustration and substituting as you read.