The idea feels like sci-fi because you’re so used to it, imagining ads gone feels like asking to outlaw gravity. But humanity had been free of current forms of advertising for 99.9% of its existence. Word-of-mouth and community networks worked just fine. First-party websites and online communities would now improve on that.
The traditional argument pro-advertising—that it provides consumers with necessary information—hasn’t been valid for decades.
Another example of that is Pyongyang. They do have billboards to Kim Jong Un, and memorials to Kim Jong Il. But, for the most part the city is free of billboards. It’s really strange if you’re used to modern western cities.