One way to start an essay is to deconstruct the use of the term "manipulation." The very term suggests that all external influences on one's opinions are by necessity bad. In fact, we can not prevent our opinions from being affected by things outside ourselves, and often that is a good thing.
We do not start life in some sort of pristine state of unfallen wisdom. We are all born ignorant, illiterate, incapable of reasoning, and ill-informed, what Locke called a tabula rasa. The duty of our parents and our teachers is to shape or manipulate our opinions and behaviors so that we can survive in the world. We gradually are taught opinions concerning the badness of theft and murder and the dangers of walking out onto the street or touching electrical outlets.
As we grow older, we must make decisions about increasingly complex topics, and make judgments about what sort of ideas will influence our own thinking. On medical topics, for example, we might be influenced by social media, television shows, pharmaceutical advertisements, doctors, salespeople, and friends. All of these are forms of manipulation, or external influences on our behavior. While we cannot escape all these influences, what we can do is choose among them consciously, rather than adopting as our own an opinion that may not be well-grounded in fact or in our best interest. The doctor or friends who try to manipulate you into quitting smoking or the MADD campaign to prevent drunk driving are positive forms of manipulation, while most advertisers, focused on selling their own products, may not have your best interests at heart.