Full disclosure: I do have a Facebook account. But if you aren't already one of my Facebook friends, and if you aren't a personal friend, at this point you might as well not bother sending me a friend request, because I'm rationing my acceptances severely. In fact, I don't know if I'll continue on Facebook over the long term, so it might be counterproductive to accept more friends.
There are so many things one could say about problems with Facebook that one could write a very long post on the subject. Covering all of them won't be my goal here. The spam issue alone has nearly driven me to shut down my account; I know how to be careful about what I click on, but some of my friends do not, and this causes things to show up on my newsfeed that I never want to be even that close to.
One of the chief reasons why you should, in my opinion, discourage your friends and especially your children from having accounts with Facebook (or Twitter, etc.) is because of the erosion of a sense of privacy.
People who grew up in the pre-Facebook era have a natural, I'm inclined to say a God-given, sense of privacy. Simply put, you don't want everyone or just anyone in the world to know everything about you. "Sharing" is not an end in itself, and the idea of sharing all the details of your personal life and your deepest thoughts with total strangers causes warning signals to go off. This is healthy. This is a normal part of the sense of self-protection. At the most basic prudential level, the human desire to preserve privacy protects one from attackers, stalkers, and identity thieves. At the professional level, a sense of privacy can prevent young people from leaving a pixel-trail that prospective employers can read containing photos of themselves and all their thoughts and religious, political, and professional opinions from their youth upwards. But beyond the obvious (or to some, disconcertingly not-so-obvious) practical benefits, there are psychological and interpersonal benefits of a sense of privacy as well.
The share-share-share culture undermines the sense of privacy directly. Default settings on Facebook share all your information with "friends of friends." Facebook's bots tirelessly suggest to you that you "friend request" more people and that more people "friend request" you. Games and apps. pop up in your newsfeed suggesting pointless and even offensive interpersonal interactions. ("So-and-so answered a question about you. Click here to see what he said." "Would Jackie ever get involved in a street fight?" "Do you think Joan has a crush on you?") If you post a picture of your family to Twitter, anyone can retweet it anywhere, so that the name, birthday, and picture of your adorable two-year-old can very easily end up being viewed by anyone anywhere in the world. (Again, even from a practical perspective, I am constantly struck when dealing with bills or medical appointments by the use of date of birth as an important piece of identifying information. Don't "tweet" your wife's birthday!)
The barriers are down. The sense of self-protection is regarded as unnecessary and paranoid. "I have nothing to hide" is considered admirable. But you should have something to hide. That's why people wear clothes. Social networking urges us to be metaphorically "naked" around large numbers of people.
Interpersonally and psychologically, here is what this can very easily mean: Suddenly, the user of Facebook has a very intimate "friendship" with a lot of people he has never met. He shares with them his passing thoughts and tons of information about himself and his family, with photos, which are recorded for as long as hard-drives spin and which can be read and viewed over a period of months and years past by anyone whose friend request he accepts. Conversely, he knows all about these other people--all their thoughts, what is bothering them at the moment. Instant intimacy is set up, and if one goes on accepting large numbers of friends, this can easily lead to a feeling of "intimacy overload." Irritations arise when your friends say things you don't agree with or vice versa. You can find out things you never wanted to know about people. There are limitless opportunities--far more than in ordinary face-to-face life--for fights and antagonism. If you scarcely knew someone before accepting him as a Facebook friend, you have just made yourself vulnerable to a comparative stranger, and vice versa, to an extent that used to be possible only over months and years, if ever, between two people.
Facebook deals with privacy by giving you "privacy settings." Mind you, even finding all of the relevant settings is daunting, and they change frequently. If you don't want insane and utterly unexpected "sharing" of your information without your knowledge or consent, you have to be constantly on your toes, and advising a new user about all the settings he needs to change is impossible unless you have a photographic memory or keep an on-going list. But beyond this, the very idea that privacy in this context can be created or restored by a setting is misguided. By its very nature, electronic social networking is anti-privacy. Its whole point is the sharing of information, the development of large numbers of instant and almost shockingly close relationships. No privacy setting can change this fact.
In fact, social networking is based on an advertising approach, as if you were trying to sell yourself. By the miracle of modern technology, it is now made easy for you to "connect with" as many people as possible in as short a time as possible and to tell them all about yourself. That would be great if you were a product. Someone selling a product wants to get the word out to as many people as possible in as short a time as possible. But you are not a product. You are a person. And telling everybody all about yourself as quickly as possible should not be one of your goals in life.
For that reason, if you have not already been drawn into the world of social networking, I urge you: Don't do it. Do as I say, not as I do. And if you've already been drawn in, hold it lightly and be prepared to let it go in the end.
Privacy is not a setting.