Easterbrook makes the same errors in logic that other people also lacking vision make. Quoting Carl Sagan out of context doesn't aid in making his point, either. For years Sagan argued against manned space missions as being more costly and unreasonably dangerous when compared to robotic exploration.
He also did say a Mars mission couldn't be "justified" by a quest for scientific knowledge alone. But Easterbrook misses the point--or evades it--entirely. The only valid justification for the undertaking of any mission of this type is if, in doing so, we cooperate with the Soviet Union in a joint mission.
In doing so we will learn to trust them and they will learn to trust us. Working closely during mission planning, development, and construction of spacecraft, and co-manning a three-year flight will, if nothing else, enlighten both sides. It will be as if we had a benign common enemy to rally against (the technical demands may be more than benign). The psychological effect of this will be to bring us together and back from the brink of nuclear confrontation.
As to costs, the costs of the mission could be evenly divided between our two nations and any others wishing to participate. This could even be the grounds for an arms agreement--we could not afford both an arms race and a space project of this scope. Therefore, if we are working together, we will know the other isn't continuing to build expensive and useless additions to an already bloated arsenal.