There are numerous restrictions placed on advertising by business firms. One example is the recent ruling by the FTC which prohibited several food producers from advertising that their products contained no cholesterol, even though the claim was true. The FTC's argument was that people might be misled into thinking that the products weren't fattening. Such restrictions would be unconstitutional if imposed on the editorial pages of a newspaper. They should likewise be recognized as unconstitutional when imposed on the advertising pages.
False advertising is clearly harmful.
However, interfering with freedom of the press is even more harmful.