The brilliant astrophysicist Sir Fred Hoyle believed the universe existed in a steady state forever and had no beginning. But his view, once held sacrosanct by all astrophysicists, no longer holds. It's been superseded by the Big Bang theory that the universe had a beginning and is still expanding.
In the 20th century, some of the most respected scientists in the world, including Nobel Prize winners, believed in eugenics—the reprehensible idea that the human race could be improved by selective breeding. The National Academy of Sciences, the American Medical Association, and the Rockefeller Foundation supported it. By the middle of the century, it had been thoroughly rejected as quackery. No reputable scientist would have anything to do with this idea.
So, we all need to get over this notion that just because someone—be it a politician, a bureaucrat, or even a scientist—employs the phrase "science says" means whatever they're saying is right.
It might be right. But it might also be wrong. And if it's wrong, it won't necessarily be a bunch of scientists who say it's wrong. It might be one guy.
Ask Einstein. One hundred scientists wrote a book explaining why his theory of relativity was wrong. He quipped, “If I were wrong, then one would've been enough.''
It takes a lot to convince scientists to accept a new theory, especially if that new theory refutes what they have always believed—in some cases, what they've staked their entire careers on. As Richard Feynman, one of the most eminent physicists of the 20th century, famously said, "Science is the belief in the ignorance of experts…" What Feynman is saying is that a good scientist should always maintain a healthy amount of skepticism. Science is, by its nature, provisional. Science would stagnate if we merely accepted proclamations of past authorities.
So how do we do good science? This is not a new question. Since the 17th century, scientists have employed the so-called scientific method to guide their work. It's not a perfect guide by any means, but it's pretty darn good.