If human free will, is not impregnable nor invincible, could that most independent feature of humanity be removed or diminished to a level of utter irrelevance? If free will could be manipulated and create a illusion that the target's choice is their own when in actuality it was a choice made an exterior entity, then the age old argument of free will vs. predetermination could be answered with the unsatisfactory answer: both. It is not as far fetched to believe that free will is malleable since that is what advertising, marketing, public relations, and political consultant firms are all paid with the fact that choices could be changed en-mass. Edward Bernays pioneered persuasion via mass media, convincing the public to support World War I and that a healthy breakfast should always include some form of pork (bacon, sausage, ham, etc), without knowing the neurological reason for the effectiveness of his persuasion; I could only assume that the psychologists, linguists, neurologists, endocrinologists, anthropologists, sociologists, and a bevy of other lab coats within research & product development of companies manufacturing consumer goods will at some point perfect means of persuasion.
Jeremy Rifkin (RSA animate video embedded above) in his "The Empathetic Civilization" has the optimistic view that with neurology discovering neural mirrors is proof that humans are designed to be empathetic, but ignores that this same fact could be used for nefarious purposes such as creating empathy for brands and companies even if it is impossible for that empathy to be reciprocated. If you are saying that some sort of brainwashing could never be attempted, that no one would have the gall to do so, then you would be surprised to find out that of your grocery store is filled with end results of the primordial of exactly that 'brainwashing'. With artificial mechanical mouths to judge exactly the optimal crunch from potato chips (4 pounds of jaw pressure); chemistry to determine the proper placement of magnesium carbonate within the chemical structure to create a sensation of bliss from a cookie; conjoint analysis done by consumer psychologists to see the combine affect of food coloring, texture, taste, packaging, and an ad nauseam number of other factors to attain the highest level craving (an euphemism for addictive if only psychologically speaking). The oligopoly that provides a vast majority of American calories could even use the captured market to make American society to be more receptive to be swayed, with the intentions that they would be able to make occasional customers converted to heavy users. Not that I am validating the Twinkies defense, but there is scientifically proven relationship of nutrients and general moods along with a hegemony of media that trains our brains to be less contemplative and interactive content that reward rapid response than delaying of gratification, all lead to more persuadable population.
Advertising's does not have an exclusive intended purpose, it is not merely to raise awareness of product or service to persuade patronage, it also provides the carrot to journalists employed by the same media conglomerate or non-profit organization (PBS & NPR receive corporate sponsorship) so that their respective news division shows difference when making editorial decisions. The same oligopoly of manufacturers and food processors for consumers along with retailers are the chief financial backers, through advertising, of the watchdogs of journalism that should be warning those same consumers of ill health effects of long-term use of those products. The 'free' press may trepidatiously refer to concerns about consumer products but would be wary to present any facts that are detrimental to a major advertiser of the parent company since there wouldn't just be loss of revenues from that advertiser but all the other advertisers would be made aware that that particular watchdog "bites the hand that feeds him". This conflict of interests is not limited to news divisions, entertainment divisions of media conglomerates also would not be welcoming of subversive unproven directors, writers, actors and actresses no matter how talented will not be given a chance to share their worldview. While at the same these conglomerates provide opportunities to those that lack any talent but co-opts the correct message (1/2 News Hour was a response to Jon Stewart success in satirizing the consumer culture after a career of being an apolitical stand-up comedian and transformed The Daily Show from a low rated satire of local news)
With the field set, the consumer deluded that the products and services they purchased was result of their own choice, barraged by media that has pseudo-colluded to a culture intended to persuade their audience, a nearly uniformed culture that buttresses the notion of consumption, there are in my humble opinion a significant segment of the population that has their free will diminished and are less able to make their own choices. It is technically possible to increase the power of persuasion of advertising along with other means and the research is on a track that will further increase that capability. It is likely that the limits of the research may come short of eliminating free will for all of humanity, but a little over a hundred years ago most people were adamant that humans could never fly through the air.