As to the Which Preschoolers Go situation, I would indeed pick three preschoolers over five. If you do not make the choice, the maniacs will kill all of them.
And as to Obama and McCain, and the murders they are both going to commit after they are elected, I have to admit, you are almost certainly right in the hard facts you suggest. One or the other of them is going to be elected by some large number of voters in this country, and they will then go forward and commit their mass homicide. There is nothing we can do to stop it (without risking our lives, and without chancing an infinitesimally low probability of success).
You are also right in your implication that John McCain is more likely to use nuclear weapons or be more belligerent.
I disagree with you about whether or not Obama or McCain will ultimately kill more people or cause more damage worldwide, because Bill Clinton was very successful at doing both of those things--he simply did it in a more cost-efficient way. But I'll put aside that objection for the moment, and accept what you say: that McCain would be worse than Obama.
So back to the main point: voting for Obama is simply an attempt to prevent McCain's version of madness from taking control.
But here is the crucial difference between choosing Obama in this situation, and choosing him in the preschool situation: the preschool hostage situation is one time only. The presidential farce is recurring.
Imagine the preschool example, but this time imagine that it happens every day. (This isn't an extreme stretch; considering how many dozens or hundreds of thousands of innocent children both Obama and McCain are going to kill, 3 preschoolers a day is probably inadequate for comparative purposes. But let's just use it.) Every day, you go by the preschool, and every day the madmen execute either 3 or 5 children--your choice.
At what point do you stop choosing? At what point do you stop playing along with the insanity--putting the lotion on the skin for Buffalo Bob--and say, "Enough."
At some point, it becomes apparent to you that the game is never going to end. The children are going to keep dying--there will always be new madmen willing to take the hostages, make the speeches, and carry out the killings. Choose your decade. Choose your war. Choose your murders.
How long can you justify this morbid farce? How long will you play the terrible game with the killer? Go back to Vietnam, if you like. Go back to Hiroshima and choose which national leader you want to press the button. Go back to the invasion of the Philippines. Go back to the Mexican American War. Count the bodies.
Is it ever going to end? Are you ever going to say, "Enough"?
Every day you walk by the school. Every day the madmen are there.
When are you going to stop giving them what they want? When are you going to stop validating not only their deaths, but their entire horrific game?
It will never stop unless we stop it. If we keep supporting it, year after year, always justifying it as "a little less murder than we could otherwise commit," it will never end.
When you refuse to vote, or vote for someone else, you are a grain of sand. But at some point, change has to happen, and it will take individual people willing to refuse to support the killing. A few crazies, at first. Then maybe, someday, more. It's as daunting a task as getting blacks the right to eat at the lunch counter; maybe more daunting, since Europeans were murdering one another in wars when they didn't have Africans around to enslave. But it has to happen. Individual humans need to be able to make the decision to stop the killing. You can do it. You can stand for peace and justice--you can refuse to play the terrible game of choosing who will die, and in what quantity. Leave the sadists with nothing but their own fantasies, and they will shrivel away.
If everyone is afraid to take the step away from killing because "it will make no difference; I'm only one person" then no one will ever step away. And the killing will never end.
(Short answers to specific questions upcoming!)