Advertising: Positive or Negative? in In My World

I'm writing an essay in English about the effect of advertising on the population and whether that effect is negative or positive. I was wondering if some people here could give me their opinions and examples of where advertising was used positively or negatively.

I already have a few examples but I can't decide if I want to write that advertising is positive, negative, or neutral(both). Any help would be much appreciated.