What if you're advertising the historical equivalent of a vacuum cleaner over a brush? A dishwasher over washing up liquid, a car over a carriage, a savings fund that invests ethically over one that doesn't, a cheaper, faster municipal broadband over a monopolistic inferior broadband, the examples are innumerable. A progressive political party over a corrupt incumbent?
I agree in general that advertising should be curtailed from the present level, but I don't agree that it's fundamentally unethical.
If you've got to rely on word of mouth, even with the internet, it will take a lot longer for good, useful products/ideas to spread.
If advertising were vital for learning about new products, nobody would use open source software. Nobody would use Hacker News for that matter. They do, which should tell you there's something wrong with your theory.
Hacker News is literally advertising / lead gen for YCombinator.
Apologies for yet again picking a nit, but PR doesn't involve paid placement of a message. Neither does lobbying, media relations, inbound marketing (Hacker News), messaging, positioning, or getting an intern to stand with a sandwich board through the street. You could run a coach and horses through that definition of advertising.