I think it's very important that scientists make policy recommendations, but they need to say where the science ends and where the policy recommendation begins. On the clean air standards, I thought the Clean Air Science Advisory Committee did a very good job. Now you, Congress, need to decide at exactly what level you want the standards set. That is a policy decision. While Members of Congress very jealously guard their prerogatives, they weren't happy to hear that this was being thrown back at them, but that was the right way to approach the issue.
Scientists usually think about science in terms of their discipline or subdiscipline.
Members of Congress usually think of science as an integrated, undifferentiated whole, except in terms of budget funding. But Members need to become more familiar with those sorts of divisions. The underlying point is that these debates at the intersection of science and policy also affect, in the long run, the sense people have of the scientific community, the scientific process, and the academic community. They also have an impact on Congress' willingness to fund science. I have two thoughts in conclusion.