What is the notion of social interaction? What do you mean by normal and healthy? I disagree that the scenario you laid out is necessarily true. It is possible though, yes.

I curate my friends list and often prune connections I have drifted away from. The friends I keep on FB are people I want to continue to be friends with. Because people were on my friends list and I saw them online in my periphery, I was more comfortable reaching out to them when I visited their cities after many years. Granted, there are some people who were, and will remain casual acquaintances - but having or not having them in my feed has no effect on me that I can tell.

So I do not think being able to keep tabs is an argument for passive consumption of people. Indeed, it has helped me actively reconnect. I do not agree that using FB is delegating an ever increasing portion of my social existence to the "black-box of the Zuckertron". I do not use FB as a substitute for people I can connect with in person. I also think you are mis-characterizing my argument under the influence of your feelings about FB.