It doesn't make sense for people to trust the service at all unless you assume one of two things:
1 - Despite all the outrage on hackernews, and the NWT stories, our neighbours down the street and family members still don't know how Facebook works or what is done with their data
2 - They don't care about their data privacy. I've heard this claim many times, but the people saying it often change their minds when they read more news stories. I really do think people have trouble assuming the worst about the intentions of others and are inclined to be trusting.
edit: clarification