I think that it depends upon the medium. Print advertising can be quite informative: detailing which products/services a company offers, product features, current pricing, and other such stuff. Business websites are pretty much the same idea. Even online storefronts are advertising (analogous to the mail order catalogs of days gone by). Of course you need to balance it out with independent reviews since advertising is intrinsically biased, but at least it lets you know what's out there.

Most TV, Internet, and radio advertising is a different story though. It's mostly meant to capture minds, rather than provide information then let the consumer consciously decide. In that sense, it is poison for the mind.