Consider "advertising" as shorthand for "paid promotion" i.e. "lying". Why would product or service discovery require the people making recommendations to take money from the producers they're recommending? How could that ever result in a world where customers receive anything but the worst possible recommendations?

Word of mouth: fine

Product on a shelf: fine unless you made a deal with the manufacturer/distributor to put it prominently rather than believing it deserves to be there

Taking money to give an endorsement: Bad. That makes you a liar.

It's the dishonesty at the heart of almost all advertising that makes it bad (well that and the often accompanying implicit push for people to frivolously consume).