I deactivated my Facebook account long ago because of this feeling. I think what it boils down to is that I don't think I should know so much stuff about my friends, family, co-workers, etc without having obtained that knowledge by directly interacting with them in meaningful ways over long periods of time. The Facebook model appears to let me know people better, but it's in a shallow, passive way and encourages me to conceptualize people as caricatures, assembled from a handful of their most obvious or outstanding personality traits. I realize this stuff has been around for a long time, but FB turbo-charges it, and I feel like it's an extremely poor way to "know" people.
The really messed up part is that while the effects Facebook seems to have are often anti-social (think of how many times you've been out with someone and they're too busy checking status updates on their phone to carry on a real, actual conversation), people are labelled anti-social for not participating.