I used to think there were useful ads. But really, even a useful add is an unsolicited derailing of your thoughtspace. You might need a hammer, but did you really have to think about it right then? I think back to how my parents and grandparents got their goods before the internet. If they needed something they went to the store. If they were interested in new stuff that might be useful thats coming out, they'd get a product catalog from some store mailed to them. Is a product catalog an ad? Maybe, depending on how you argue the semantics, but its much more of a situation like going to a restaurant and browsing the menu and choosing best for yourself, vs being shown a picture of a big mac on a billboard every time you leave your home.