The danger here is that people are misled by dishonest people who push up sales of useless things. People think that, whatever comes in print is true. They also think that when a thing is said to be good, it must be good. The advertising people are familiar with this psychology of the customers. They know that if a lie is repeated a hundred times, it sounds like truth and after a while it is taken for truth. This strategy is dangerous for public health and consumption standards.
Furthermore, unscrupulous advertising attempts to vitiate the psychology of potential buyers. They do marketing of such goods which adversely affects human health and environment. For, it is not rare to meet with such instances where advertisements play foul with the potential buyers. Such type of advertisements misleads the buyers. It attempts to put them at confusion to gain more and more benefits.
All this is not to suggest that business of advertising is an unmitigated evil. Put to proper use, advertising can do enormous good to society if used properly. However, in the hands of those businessmen who are unethical and unscrupulous, the chances are that advertising will be more an instrument of individual and social harm than an agent of human welfare.