In what sense are you claiming advertising is negative sum? Who is meant to come out behind? The business buying advertising is ahead, the ad company is ahead and the consumer has something they decided they wanted. I see a lot of ads that are a mild waste of time because what they are selling isn't something that I'm buying, but that isn't negative sum. They are usually present in the context of free or subsidiesed services.

Advertising isn't a crazy form of mind control where people are hypnotised into handing over money. Sure that might happen, but the vast majority of people I've met don't know they have a problem until it is pointed out to them.

For example, in '07 I didn't find out about smartphones by word of mouth. I found out because Apple put a lot of effort into some very effective marketing. And there is pretty good evidence that the advertising industry is one facet of a larger apparatus developed to make sure that messages make it to the local word-of-mouth circles.