Paid online advertisement on sites belonging to other than the producers, advertisements listing engines, or the local administration, is a category of spam and should be outlawed. In terms of today only Froogle-like sites or passive/administrative listings of services/products offered by the entrepreneurs should be legal to exist.
That is because: 1. it's consuming the involuntary reader's bandwith (especially the graphics) and that costs money; 2. it's cluttering the sought after information with garbage (especially the text ads) and it consumes the involuntary reader's time, which also costs money; 3. it mixes the marketing power with the real qualities of the products offered; and this gives a huge advantage to monopolies, that is, delays or kills any alternative new solutions, that is, it results in a monoculture and a society of flat brained morons, that is, it goes against any notion of free market economy (if that ever stood for something); 4. it damages the visual and auditive sensibility of any human receiver, as well as his discernment.
These points are aggressions commited on members of the society, at random. This is nothing less than violence, and, as such, it should be stopped.
If this continues, our society builds on distorsions, and any member of it is bound to feel the consequences, one way or the other.
If you publish paid advertisements for things you don't produce then you are a dealer or reseller, so anything else you have on your site is a fake: a masked intention to make the reader to spend his resources on something he wasn't looking for.
Restricting, by law, the paid online advertisement doesn't affect anybody's wish to put links to products/services they prefer personally if they are done for free, not for a fee.