I see the following issue:
What is an ad? Is it an ad spot in the middle of a TV show? A big billboard? A banner on a website? Someone talking about a brand? Just writing or saying a brand name? Subtle algorithmic nudging?
You gotta put a line in the sand, and depending on where you put it, it'll be harder to influence anyone or harder to address brands or products. There's always a trade off.
And then additionally we gotta address any behavioural adaptions of big companies. Imagine if companies started striking illegal deals with social media companies for favourable algorithms? How do you control that? And on the other hand, imagine you were talking about a product and suddenly people accuse you of illegal advertising? How do you make sure people don't skirt the line and also no one is wrongly convicted?
I'm not saying this is a dumb idea, I actually agree cracking down on forceful or manipulative advertising is an interesting idea, I just think that these broad stroke ideas an insane amount of continuous planning, validation and readdressing.