Groups on the political fringes like to quarrel with science. Some of my fellow travelers on the political right regularly reject evolution and certain findings of climate science. A portion of the political Left, likewise, insists on fighting effective pesticides and vaccination -- often with deadly results. In short, neither party can honestly say it has exiled the anti-science crowd and no party can claim to have the "scientific" answers. And that's just as well. Scientific truth must inform public but simply being right about science doesn't -- and shouldn't -- always provide as much evidence as one might want as to the solutions to complex public policy problems.
Indeed, the problems most easily solved through mere understanding of science aren't all that important. It's certainly desirable that citizens be informed about scientific facts and a rudimentary understanding of the facts of evolution should be part of every high school curriculum. That said, the problem -- understanding evolution -- isn't all that important. Nobody has ever died because they were ignorant about evolution and, unless one wants to work as a biologist, it probably isn't necessary to living a good life. A free society, obviously, must let parents and private schools choose to teach "creation science" even though it obviously isn't science at all.
As things get more consequential, however, the public policy solutions become more difficult. Vaccinating all children against deadly infectious diseases prior to school is certainly a good public health policy. But respect for individual and parental autonomy has long allowed parents to opt out of medical treatments for religious reasons. And this is as it should be particularly when it comes to preventative rather than curative therapies. And some vaccinations -- against chicken pox and conditions that may lead to late-in-life cervical cancer -- do seem to have cost/benefit calculations that ought to render them less-than-mandatory in any case.
And, when the science -- as in the case of climate change -- reflects on future events with potentially vast but unknown consequences, the calculus becomes even harder to work out. While it's easy to show that climate change is real, human caused to a significant degree, and likely to have a number of negative future consequences, the public policy solutions aren't answerable by scientific means alone. For example, there's no scientific answer to questions about the likely progress of future technologies, the way adaptation measures would (or wouldn't) work, the level future of economic growth, and the most desirable tradeoffs between growth and environmental protection. And all of these are major concerns.
Putting scientists alone in charge of public policy on complex issues, then, is counterproductive. Being able to explain how radiative forcing works provides only very limited insights into the overall costs and benefits of, say, a cap and trade scheme. Scientific training per se gives no insight into economics, public opinion, proper social policy anything else. In the end, the United States is a small-l liberal democracy, not a technocracy. Suggesting that scientists alone should make decisions is a rejection of democracy.
Science has a major and important place in public policy. But a correct understanding of science doesn't necessarily shed as much light as some might wish on complex public policy issues.