"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?
And why should they consider 3^^^^3 differently, if their function asymptotically approaches a limit? Besides, human utility function would take the whole, and then perhaps consider duplicates, uniqueness (you don't want your prehistoric tribe to lose the last man who knows how to make a stone axe), and so on, rather than evaluate one by one and then sum.
The false allure of oversimplified morality is in ease of inventing hypothetical examples where it works great.
One could, of course, posit a colder planet. Most of the population would prefer that planet to be warmer, but if the temperature rise exceeds 5 Celsius, the gas hydrates melt, and everyone dies. And they all have to decide at one day. Or one could posit a planet Linearium populated entirely by people that really love skydiving, who would want to skydive everyday but that would raise the global temperature by 100 Celsius, and they'd rather be alive than skydive every day and boil to death. They opt to skydive at their birthdays at the expense of 0.3 degree global temperature rise, which each one of them finds to be an acceptable price to pay for getting to skydive at your birthday.