> Also it would be more efficient to do semi-targeted advertising by buying space in related places: magazines related to your product, sponsor spots in youtube videos, ads in specialty stores, etc.
Those are all still marketing. Whether they're better than billboards depends on what the product is.
> You won't have the money to buy such billboards anyways.
Billboard space is available starting at on the order of $1000/month. This is well within the reach of a small business for a one month campaign and the dynamic billboards will even sell space on an interval of 15 minutes.
The fixed billboards in the most expensive cities are all Coca Cola and McDonalds because those cost the most and that's who can afford them, but the proposal is "ban all marketing" not "ban all marketing by multinational corporations".
The latter might be a good time though.