Yes, the purpose of ads is to convince people to buy things that they otherwise may not. But shouldnt that be a positive thing, more often than not? Traditional reasoning would suggest that someone buys something because it improves their lives, so selling it to them is a positive act.

I had a startup that made PowerPoint collaboration software, and we advertised on Google for terms like "work on presentation at the same time" and "PowerPoint collaboration." We got almost all of our users from Google, and most of these users were thrilled to find our software which they wouldn't have been able to find without targeted ads.