Is it ethical to use brain and psychological data to try to alter consumer behavior?

Marketing is centered on the idea of influencing consumers to purchase products or services. Marketing in our day and age has developed more effective strategies and utilized better consumer data-collecting technology than ever before. However, not many people think about the consequences that these improvements may have on the consumer. Is it ethical to use brain and psychological data to try to alter consumer behavior?
Let’s first look at the job of a marketer: to get inside their customers’ heads and make them want to buy products. One of my favorite advertising strategies that accomplished this was the 99 cent KFC Snacker television ad in 2009. The ad had a hidden image, a tiny dollar bill, located in the lettuce of the Snacker (approximately 50 times smaller than the sandwich itself). Its purpose was to subliminally express to the minds of consumers that the sandwich held many times greater value than a dollar (associating size with value when the two were compared). Think about it this way: one tiny dollar for one large sandwich. This ad, due to a value-association strategy that KFC subliminally introduced, garnered lots of attention.
Marketers like KFC want to influence you into selecting their products, but is it possible to take go too far? If one markets a product and the consumer behavior is altered to impose upon free will, then it is NOT an ethical practice. In contrast to KFC’s success, a study was compiled by the United Nations, and they concluded that subliminal indoctrination is a major threat to human rights (Slatkin). Fortunately, the Snacker ad is ethical because it merely suggests a correlation between the tiny dollar and sandwich—resulting in value as seen by the public. It may be using subliminal imaging, but there is hardly cause to label it