Here's my take: When someone goes to the search bar and Googles the key terms they're in need of answers to, they are on a mission. When someone is on Facebook, chances are, they are not on the very same mission. There might be times where they are, but Google is still a widely used search engine while Facebook is social media for engaging.
This is just a screen capture of a few of the images that came back in my search.
This confirmed a bit of how I feel that some people will perceive ads on Facebook, because they're not seeking them out, they're just present, regardless of whether the user wants to see them or not. Although on the positive side, they are targeted and should provide relevant ads. But they're unsolicited nonetheless. I do know people who claim they've gotten business from these ads, so I am not completely averse to them, I just want you to look at all options.
Along the right are ads: one for snowmobiling in Maine, one for Ultra Sport socks, one for Trulia Real Estate and one for Mercedes.
Are these relevant? If I am looking at the beautiful art glass Linda is working on, am I going to click on one of these ads?