Warning: INCOMING RANT!! Don't take it personal!
FB, Twitter, Pinterest, Instagram, etc... They are free for a reason. And people who think they are there for us, are ignorant.
WE, the users, are the PRODUCTS, they sell. It is in their own best interests to know as much about us as possible. So, yes, they look at your contact lists, phone numbers being called, phone numbers receiving calls from, what website cookies are on your phone/tablet/device, how long you look at your feed, which posts you stop on, which you respond to, who the contacts/friends are of those people, what their interests are, what groups you visit, what locations you visit, at what times, what apps are on your phone, how often you use them, etc...
Every piece of data that you don't deny them, is a piece of data they collect. They gather that data and build composite demographics on every user. They then can sell their marketer/sponsors premiums for targeting ads at you.
Based on your choices, such as where you buy from online/in stores, what you "Like", when you are travelling, when you check-in, who you are in photos with, they can match you up with like minded people in your area. If you "Like" a movie, they look at all other people who liked the movie at about the same time, in the same area, or even the same movie theatre. If they share "X" qualities, then you may know them.
If you say you do, or you accept the friend request, then their contacts, friends, places, etc... become attached to you as well. Even if you unfriend/unfollow them, the connection is made and considered.
It doesn't matter whether you publicly post this information or limit it to just friends, the fact is that you revealed the fact to FB, Instragram, Pinterest, Twitter, etc...
By the way, I'm no conspiracy theorist. We all know, going into the arrangement that we are the PRODUCT, not the consumer/customer. Who ever heard of a bottle of ketchup complaining about where it is placed on the shelf?
The social media platforms aren't evil. They are business. They are insidious and very good at what they do. They are extremely effective and sell a very complete product to their customers. That very complete picture of us and our lives.
The social media platforms serve some good. They provide a stage for people to voice an opinion. People used to go to the town square, step on a soap box (a crate that held soap), and talk to/shout at the crowds of people. They would yell until they felt their voices were heard. SM's are no different, just a larger town square, and a written record of your words, and no rain/snow to deal with.
My biggest complaint to people are... I wouldn't go out into the square and shout "I'm not at home! I'm at the movie theatre for the next 3 hours! And so are these three friends!" I don't need the reason to share that with the all the other bottles of ketchup, or with those who don't like ketchup.
