one of the most difficult things to relay about why facebook is a danger (probably more so in years gone then now) is they can not visualize the effects (both in the real world and mentally) . This was probably how drugs where viewed back in the 70s it was all seen as fun and games and mostly harmless.
If you say to someone dont speed, drink and drive as it may cause you to get into a car accident its clear to see the devastating impact speeding and drink driving can have, people can imagine it, they can see it and dont want to be involved in it, but when you tell friends and family facebook has the potential to brainwash, manipulate and control you its hard for people to understand how because it is related to understanding how data can predict and be used understand behavior, its a very new concept for many people just being understood in the last few years.
To the majority of users they control facebook, its not the other way around, they can delete images, comment on things, vote on things and and do what they need to on the platform from the saftey of their own home, to majority of people it gives them a voice when before no one cared about what they had to say, but as the ads that they are shown seep into their thoughts without them knowing, the articles and propaganda about the latest political events change their behavior and their emotions and mental well being are affected as they see their friends lives supposedly much better then theirs, they just get more and more sucked in.
As someone with a comp sci major from 15 years ago and understanding the power of data i have been having this conversation with people for years and even now with so much of these facebook powered problems occurring more and more in the media, many still dont see the effects, though at least now , the dangers are hitting the bigger more general audience. At least there is progress there and hopefully this will allow the public to make a more informed decision before they put up their whole lives and the lives of their kids on social media before their kids are even old enough to approve or accept that they want a social media account.