You are right, but there might be initial utility to a lot of people and still have net negative effect over long time. Think of Tesco or Wal-Mart opening up in your neighbourhood. Initially it is good for everyone, then the mom&pop shops close down, then downtown loses its vitality, etc. etc.
Similarly, I don't mind Facebook doing whatever they do and being useful to a lot of people. What saddens me is how other (often superior) options become slowly unavailable.
The only option that was worth anything that I've seen that seems to have disappeared for my generation due to technology is the what I call "the meeting place". This is where, due to the lack of constant connectivity, people would designate a place that you just would go, no matter what, at certain times.
Think the Pool Hall in "Dazed and Confused" or the bar in "Cheers" for a couple pop culture examples. From both pop culture references and anecdotal evidence I've collected, it seems the "if nothing else is going on we always meet at x place" used to be more common than it is now. Now everyone wants to know who's going to be there, when, etc. before they decide whether to go.
Similarly, I don't mind Facebook doing whatever they do and being useful to a lot of people. What saddens me is how other (often superior) options become slowly unavailable.