Ads are inefficient, but are still useful as a information distribution method across inefficient markets. The perfect ad will lead to a mutually-beneficial transaction between a buyer and a seller.

There is also a cognitive bias with ads, where people on attribute negative ad experiences to advertising, never the good ones (except in super bowls or other outliers).

You can also extract water from feces, that doesn't make them a good thing.

Well I certainly haven't had a cognitive bias or enjoyable experiences with feces, but if you have then sure, that analogy works for you.