I think the smoking analogy is a pretty bad one, because smoking is an empty activity with little redeeming value. Once you quit you actually become sort of repulsed by the activity. There's very little at the core of smoking that's worth keeping.
But the core of what Facebook does is very good. Everyone I care to still be in touch with from high school, college, and multiple past jobs is there. That core feature is good, not bad.
And it's not at all obvious that those people are ever going to go somewhere else. Sure, teenagers are going to keep adopting new, fun stuff, but none of that new, fun stuff replaces that core feature of Facebook.
"Teenagers hanging out" is a different use case from "adult who wants to stay in touch with people he knew a decade ago." There's no competition for this latter use case.
But the core of what Facebook does is very good. Everyone I care to still be in touch with from high school, college, and multiple past jobs is there. That core feature is good, not bad.
And it's not at all obvious that those people are ever going to go somewhere else. Sure, teenagers are going to keep adopting new, fun stuff, but none of that new, fun stuff replaces that core feature of Facebook.
"Teenagers hanging out" is a different use case from "adult who wants to stay in touch with people he knew a decade ago." There's no competition for this latter use case.