I may be out of the prime facebook demographic by several years but even I understand the significance of this for a huge number of facebook users. A lot of people view facebook as something in the same genre of livejournal or blogger, a tool that allows you to keep in touch with friends but that is nevertheless still fairly public and limited. However, a huge number of people have taken facebook far more into their private lives. They use it as a replacement for email, for example. These people's entire digital lives are in facebook. Every sordid detail of their personal relationships. Every little bit of letting off steam about coworkers and bosses. Every piece of personal information from their home address and phone number to the sex toys they bought last week. For these people facebook's privacy settings are critically important.

To put yourself in their shoes imagine if your email provider or phone company made an announcement that they were making a change to their privacy settings. If you thought that there was a serious chance of your email, text messages, or phone conversations accidentally becoming public because you failed to tick the right checkbox somewhere you might demonstrate just the slightest bit of consternation at that prospect.

For myself I've been lucky since I hardly use facebook, and then only grudgingly (more out of a hatred for the UI than anything else), but for many of it's heaviest users facebook does not appear to be operating in, let alone even considering, their best interests.

Becuase it's not just what you put on there, it's what others put on there about you.

Plus - do you really want _anyone_ who feels like it to be able to find out stuff about you? Insurance companies, potential employers, the tax man, debt collectors and so on?

Or how about a scorned ex-gf/bf, someone you've had a dispute with etc etc.?

Basically, it makes you vulnerable.