I've heard it said countless times that science is just a set of opinions and that it is no more valid than anyone else's. That assumption underpins much of the justification for Woo theory, whether it's the existence of some undetectable energy called Qi, or some healing energy that is assumed to exist inside us, or the existence of chakras, or the apparently remarkable properties of magnets and crystals. Science, it has been claimed, is arrogant in assuming some kind of privileged access to knowledge of the world, in setting itself up as the arbiter of truth. In this view, science is preventing us from having choice, restricting us to believing only what is given to us by scientific authorities. This view even had its own absurd academic variant called postmodernism that tried to make this theory profound by using obscure, and often meaningless language.
Scientists are very used to this sort of comment and invariably it arises from a poor understanding of how science progresses. The first, and perhaps most important, principle of science is that the theories which explain our knowledge are independent of the beliefs and values of the proposer. It does not matter, at all, what the scientist thinks or believes — the theory must rest on its explanatory power and the supporting evidence. Science is not a belief system.
Secondly, it isn't science that constrains us and takes away our choice in what to believe about the way the world works. It's the world itself. It doesn't matter what any scientist thinks about gravity, or the boiling point of water. These things are completely independent of any world-view the scientist might have. The choice in what we believe is still there, but whether it corresponds to reality or not is not our choice. Nature doesn't care what we think.
Science makes strenuous efforts to ensure an accurate correspondence between theory and reality and the reason our choice is restricted is because external reality constrains us. We cannot simply decide that water boils at a different temperature or redefine the value of gravity. These are real, tangible external constraints. Scientific experiments are all about identifying and understanding those constraints.
So when it comes to talking about medicine, and whether or not some therapy works, we have to test it against the real world and not simply stop at the point when we've made up the theory. It's not scientists who are being undemocratic in restricting our choice of belief in a medicine. We can all, if we want to, believe that homeopathy works. But it's testing it in the real world that will tell us whether the theory is right or not. It has been tested, and homeopathy doesn't work. And that doesn't change just because someone spends money buying it.
Let's think about magnets, just for a moment. We can buy therapeutic magnets which, we are often told, will improve our health. But just in order to generate an MRI image, we need a massive electromagnet, the size of a small room. The reason is that in order to get the image, you have to perturb the protons in the hydrogen atoms of water using intense electromagnetic radiation. Just that tiny peturbation requires a massive magnet. Now think about the size of magnet that fits around the wrist and what effect that is supposed to have. This is not opinion, or someone's point of view. It's the real physical world dictating what is actually possible — irrespective of the opinions of any scientist. The peddlers of these magnets won't explain how they think they will work — because they are constrained by the physics of the real world. It's in their interests not to know.
One of the reasons scientists are so often maligned is because companies often cite pseudoscientific arguments to support the sale of products, and the media sensationalise the typically cautious scientific claims. In that context, when we distrust the products (because marketers almost always hype), we also distrust the scientists. We are often right to distrust scientific results, especially when they are produced by institutions which represent commercial interests. Science that doesn't meet a high standard of evidence, subjected to open peer review, is unlikely to be trustworthy. But that doesn't mean science is just opinion. It's actually the opposite. It refuses to accept opinion as sufficient, it doesn't accept a person's word or belief as sufficient, it doesn't accept anecdotal biased reports as evidence. It demands a test against the real world. And when it's proven wrong, it changes.