When you were last severely diseased or injured, from where did you seek treatment? Most likely, you were treated by a trained and licensed medical professional. Your treatment was backed by evidence of current scientific medical knowledge. Unfortunately, this does not ensure perfect recovery, and in some cases, such as cancers, cannot ensure survival. Most drugs carry a plethora of undesirable side-effects. Medical knowledge is not complete, and these “blind spots” in it are being researched to create better treatments. However, some may view medicine's ignorance not as a temporary problem being progressively solved, but as an indictment against the institution as a whole. When one or a loved one is not cured or dies despite receiving the best available treatment, antipathy can be inspired in those who believe medicine ought to be perfect (a goal, to be sure, but not feasible for now). Medicine as an economic market exacerbates such antipathy by tainting medical research's reputation: “Are they trying to cure me or make me into a life-long customer?”, but the intersection between medicine and economics is another discussion. It is enough to say here that healthy skepticism of corporate incentives can be fanned into paranoia towards all of medicine. So, where do these people go when they have health concerns? Now enters anti-science.
Interestingly, those who stand to benefit most from anti-science have the same motivation as those whom supporters fear in the pharmaceutical industry. They are the burgeoning alternative healing industry and they want to be profitable.