Not quite 0. If you participate in liking, sharing, or commenting on Facebook posts that were sponsored at some point further up the chain, then you are part of the value that Facebook offers to those advertisers. (Advertisers are paying for the initial exposure and the network effect.)

Hah, you'd think. Just because you're not clicking on ads on Facebook, doesn't mean you're not ratting on your friends whenever you use Facebook. By liking things and talking to friends, they can correlate what your friends would probably like to see and show them better ads which they are then more likely to click on. By talking to some friends but not others, you tell Facebook who is most likely to like your likes. By your message's contents, you tell Facebook what your friends like to talk about. The list goes on and on.