Launius said the arguments fall flat with many people. When historians try to understand great missions of exploration, he said, "We're essentially reduced to four 'G' words: God, Gold, Glory, and Geopolitics." Nations send out explorers when they want power or material return. "Right now, we don't have that."
Polls show Americans have warmed over time to the memory of Apollo. Since 1979, the number of people saying the moon landings were worth the cost has risen from 41 percent to 65. Launius says there is not organized opposition to the space program, the way there is to other efforts; there just isn't ringing support. Millions of Americans still question Kennedy's decision.
So we come back to his famous 1962 speech at the Rice University football stadium.
"But why, some say, the moon? Why choose this as our goal? And they may well ask, 'why climb the highest mountain? Why, 35 years ago, fly the Atlantic? Why does Rice play Texas?'"
The crowd roared.
"We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard," Kennedy said, "because that goal will serve to organize and measure the best of our energies and skills, because that challenge is one that we are willing to accept, one we are unwilling to postpone, and one which we intend to win."
ABC News polling director Gary Langer contributed reporting for this story.