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.
The phrase “ban advertising” is reductive. Different countries have different laws around ads. For example, anime shows have bumpers in them because in Japan they are required by law to clearly indicate when advertising starts and stops.
There’s also laws against billboards, against targeting children, against specific industries, and limiting the amount of advertising available. I could see laws against targeted ads like Meta uses being implemented as well.