So, this choice over how to vote should not be a decision based upon personal feelings or one's flattering desire for a perfect self-image. The American people are hiring the person who will be entrusted with the nuclear codes, who will have the power to start wars, who will decide whether to take action on global warming.
Real people in other countries live or die by such U.S. decisions. Even if some Americans feel that voting for some imperfect candidate is too degrading, too compromising, the decision can have devastating consequences for others.
Yes, there is an element of triage here, since neither Obama nor Romney would be a pacifist. Some people will die regardless of who's elected, but there can be an order of magnitude difference. There is a distinction between targeted killings of al-Qaeda operatives (even with "collateral" deaths of people in the vicinity) and the mass slaughter inflicted by fullscale war.
At minimum, it would seem to be the duty of American voters to minimize the damage that their country might inflict on people in faraway lands. Even if perfection is not an option, one of the choices is likely to cause fewer deaths and wreak less havoc than the other. It may be impossible to know the future but history can be some guide.
While this responsibility to mitigate harm to the world may seem unsatisfying to Americans who yearn for something much closer to moral purity -- and who don't want to sully their consciences with such moral relativism -- this lesser-evilism does have a profoundly moral basis.
Just stop and ask: as imperfect as Humphrey, Carter and Gore were, would the world be in a better place if they had been elected in 1968, 1980 and 2000, respectively.
Would there likely be fewer people living in poverty in the United States or dying without health care? Would American politics be more democratic and less corrupt than it is today? Would the environment be less endangered? Would science and reason be disparaged the way they are today?
Would a lot of innocent Vietnamese, Cambodians, Salvadorans, Guatemalans, Nicaraguans, Afghans, Iraqis and people from many other countries be alive today? Might they have escaped horrible deaths, rapes and maiming? While no one can say for sure, you can make a reasonable guess.
So, in the end, what's more important? What's more moral? The vanity of perfectionism when perfection is not an option or doing the imperfect thing to save some innocent lives -- and maybe save the planet?