I try to make my relatives understand that this is something important, to put forward rational arguments, but they refuse me, saying that it would only complicate their lives, so it’s useless. I’m seen as the paranoid of the gang. So how would you convince your friends?
I think you are actually on to something here. If the “much more frightening dangers” could be articulated and some examples could be added it will make for a very persuasive argument indeed. The “I don’t mind targeted ads” is the most common push back along with people not getting how their metadata being collected could be used to scam them and the fact that no one likes to think they will be gullible enough to become victim of a scam.
I wouldn’t go for illegal things people can do with my data (like scams) because criminals may use illegals ways to get my data as well. We should care more about the legal ways of acquiring data and using it against our interests.
It could still help limit people’s use of sites or sharing too much data. Just think of the “security question” often they ask you. For example Name of your first pet? Don’t have that information on social media.