... we might be as ignorant about our surroundings as we were 50 years ago, when astronomy texts still included the debate about the craters of the Moon being impacts or calderas, and the 'vegetation' hypothesis about Mars' seasonal changes. We might still be imagining jungles beneath the clouds of Venus. And we would know nothing else about deeper space than we could glean from Earthside optical (and radio) telescopes.

All thoughts of the glory of personal human exploration aside, we receive a lot more science for the dollar from "robots". And they are not merely useful, but necessary scouts. Without Ranger and Mariner before Apollo, we would not have been assured that the LEM wouldn't sink into a half-mile-deep bowl of accumulated Moondust! Without Voyager and Galileo, we might not be talking about Europa as a potential life-bearing neighbor -- and thus, another possible target for an eventual human mission.

In short: "billions of dollars of robots" trump trillions of dollars of manned craft launched in ignorance.