I believe the point is that many people have A LOT of faith in the doctor's hands, and/or "what the label says on the prescription". For some people there is an unwavering sense of "but doc told me to take this, so I must HAVE to", or even "But the doctor prescribed this, so there's no way it could harm me". So, they may stop holding themselves accountable for the drugs they're taking and may not even notice negative side effects (dependence and withdrawal included).