This doesn't match up with my experience at all.

I have easy access to photos people share with others now, so I can see pictures of their kids and the like (and see that they went to Hawaii or something). I've been able to get back into contact with people I met at an event long ago and chat with them. I hear about my friend's projects, which lets me message them.

My friends and I organise events through facebook. We can keep track of location and post pictures of the event afterwards.

The end result is I am in contact with way more people than I could manage with the friction of calling/keeping tabs on everyone all the time. It also results in a lot of real-world interaction. There are people I meet twice, three times a year and _that's totally fine_ because without a tool like fb I would never meet them. My circle of friends would be way smaller without fb.

Of course I keep contact with very close people through other mechanisms as well. But claiming that facebook results in less social interaction doesn't match up with my experiences too well