You're on a Caribbean cruise, taking a leisurely walk on the deck, enjoying the sun and sea breeze. You pause for a moment and lean against the railing. Suddenly, the devil, dressed in a rather natty tuxedo, is standing beside you.
"My dear friend," he says, "it's been so long since we spoke last. I was beginning to miss you."
"Oh, not you again," you say.
"That hurts, dear friend. In fact, I think my visits have been rather salutary---"
"And on such a nice day..."
"---and you know what, my name actually means adversary. In the ancient Hebrew tradition, I wasn't the incarnation of evil itself. I was more like a criminal prosecutor. I'm the opposition voice, which is necessary to make the system work."
"Well, I think the system outlined in scripture sounds like a terrible way to run the universe, so what's your point?"
"Simply that you should blame the guy upstairs. I'm just the hired help."
"Whatever. Get on with it."
The devil lights up a cigarette and smiles. "In ten minutes, I am going to sink this boat with a typhoon that will spring up out of nowhere. I'm also going to make all the lifeboats disappear. Everyone on board will die."
He pauses and takes a slow drag. You roll your eyes. Drama queen.
"Or, I could leave one lifeboat. Then you can save a few dozen people."
"What's the catch?" you ask.
"No catch. Choose: one lifeboat, or zero."
"One lifeboat, of course. This is a pretty trivial dilemma."
"Well chosen. Yes, it's a trivial dilemma, which is why I won't bother sinking this boat. Anyway, the tux is rented, and the dry cleaning bill would kill me. Here's the real dilemma." With a flourish, he pulls a small metal box out of his jacket pocket. The box has two buttons, labeled A and B. He hands it to you, of course.
"Now," he explains, "you must press A or B. If you press A, then everyone on this boat will die instantly. If you press B, then everyone on this boat will die instantly, except for a few dozen, who will live. If you press neither, then in ten minutes I'll bring the typhoon, and make all the lifeboats disappear. All hands will be lost."
"How about I just use this box to bash your brains out?"
"If you think you can take me..." He fades from sight, leaving only a disembodied cigarette hanging in the air. "I'm still here; I've just tucked myself into a nearly-inaccessible fold of quantum space-time. If you swing, I give you odds of one in ten billion that you'll hit me. I'm not lying. It's a nonzero probability. You've got a real chance."
You sigh. "Okay, I suppose I'll have to press button B."
The devil snaps back into view, smiling. "Excellent. Not a hard decision, since the choice is, for practical purposes, morally isomorphic to the previous one. Now, I suppose you'd call button B a lesser evil than button A. But you felt morally obligated to press it, rather than take the one-in-ten-billion chance of swinging at me."
"This is leading to some rather tedious, obvious, didactical point, isn't it?"
"Yes, but however obvious it is, there are many thousands, perhaps hundreds of thousands, of Americans who do not grasp it, so let's proceed. Give me the box."
"You're not going to sink the ship?"
"Like I said, the tux is rented. Now, here's thought experiment number three. Suppose that we're in the midst of a United States Presidential election. Suppose there are two candidates, and your assessment is that one is somewhat less evil than the other. The evil one is button A, and the less evil one is button B. There's a third party candidate who has a one-in-ten-billion chance of winning and changing the whole system, and that's probably an overestimate of the probability. What hangs in the balance? Not dozens, not hundreds, but (at least) thousands of lives and perhaps the future of the free world. The balance of the Supreme Court for the next generation. Life-saving scientific research. Federal funding for health education programs for millions of Africans. The list goes on. What is your moral obligation? Button A, button B, or take a swing?"
"Exactly." With that, the devil takes a last drag, flicks his cigarette into the ocean, and strolls off towards the bar.