Personally, I think people who say things like that, have no concept of what is going on on the internet. Yes, you can assume that you "just don't log in" or "control your privacy setting appropriately", but I can assure you, you will make one regrettable mistake one day. Either you completely shut off your information or you make yourself vulnerable on the internet (which is not a good idea, in my opinion at least). There is no in between, there is no "wise" way to use facebook.
And no, I don't say this because "it's cool to dislike popular things". I say this, because I have seen people making very sad decisions via facebook without even knowing what they are doing. No one can claim to know for sure what they are doing when they use facebook in various ways. There are just so many ways to make mistakes on facebook. I could tell you various (hilarious or tragic depending on humor) stories how facebook devastated lives, but that would probably go to far. I just want to tell you that this is no "hysteria" or "paranoia". This is very much reality, I've seen it.
Topic: Why not, I won't use it if Apple gives me the choice. I think they will.