There's nothing wrong with calling friends up, but that takes a lot of work and a synchronous connection between two people. There are hundreds of people I want to know about or stay in touch with but don't have the time to call them all up individually.

Facebook makes being friends easier. That's a pretty solid value add. I would probably lose a lot of friends more easily if I didn't have Facebook.

You may not value that, but I find it much more valuable than the value I'd gain from making sure Facebook doesn't know enough about me to show me relevant ads.