The manned space flight program masquerades as science, but it actually crowds out real science at NASA, which is all done on unmanned missions. In 2004 President George W. Bush announced a new vision for the space agency: a return of astronauts to the moon followed by a manned expedition to Mars. A few days later NASA's office of Space Science announced major cutbacks in its important Beyond Einstein and Explorer programs of unmanned research in astronomy. The explanation was that they "do not clearly support the goals of the President's vision for space exploration."
Soon after Mr. Bush's announcement I predicted that sending astronauts to the moon and Mars would be so expensive that future administrations would abandon the plan. This prediction seems to have come true.
The cost-to-benefit ratio, at least in terms of science output, is just not there for human spaceflight, and even the ISS for that matter. Decisions to do this have been based predominantly on politics, and funding appropriate home constituents. When one argues that such cutbacks can hurt science, and then to hear very prominent scientists disagree with that assessment, it kinda throw that claim into question.