In a broad (and rather optimistic) sense, advertising informs you of available opportunities, not just things that you can buy. I guess you can try to separate it into "selling products and services" versus "brand promotion and awareness" versus "public service announcements", but the line can be fuzzy and gray.

I don't have anything against ads on webpages in general, but I really hate anything with sound/animation or focus-stealing like pop-up/interstitual/hiding/whatever. I don't block ads because I'm lazy, and because I think it's an acceptable payment model for content, but I just leave the page if the ads annoy me enough.

FWIW, the only ads I've actually purchased services/products from are when I'm actually searching for them and they come up as sponsored results or sidebar ads.