@DrewDad,
Perhaps, but my dissatisfaction with this hypothetical is that it is too pat.
People have been attempting to manufacture additional options, but only two exist:
1) You push the button and kill 20 million, but save 6 billion.
2) You don't push the button and 6 billion die.
You don't get to not push the button and hope the 6 billion death scenario doesn't actually materialize. Other than being delusional or mentally defective there can only be two reasons not to push the button:
1) You refuse to be the direct cause of anyone's death
2) You want 6 billion people to die
Sentience is free to posit whatever dilemma he wishes, but a realistic moral dilemma would not have such certainty of outcome.
The "Torture the Terrorist" dilemma when presented, usually attempts to strip away all uncertainty so that people will be confronted with the choice of upholding a moral position they have taken in the abstract (never torture) in the face of a certain greater evil (the death of hundreds or thousands).
Frankly I never believe the people who say they wouldn't torture the terrorist, but if they are being honest, I hope they never have a position of authority anywhere in this nation.
However, the decision to torture will almost never be made in the context of such certain circumstances.
Even if the terrorist has admitted (without torture) that he has planted a bomb, there is no certainty that torture will reveal its location and with time to disarm it. There is also no certainty that he has told the truth about the bomb in the first place, that it will actually detonate or will even kill anyone.
If the recent would-be Times Square Bomber had been the featured terrorist in the dilemma, torture may have led to his revealing the location of the SUV, but ultimately it would not have made a difference. His device never detonated.
Don't get me wrong, I still would have most likely opted for torturing him, but it wouldn't have been as easy a decision as this hypothetical allows.