Facebook Ate My Address Book

Violet Blue, reporting for CNET:

When Facebook forced its hundreds of millions of users into an @facebook account, commenters across the Internet talked about alterations that had begun in their contacts and address books outside Facebook - valid e-mail addresses were being changed for @Facebook without people's awareness or consent on their phones and computers.

I'm starting to think Apple baking Facebook into iOS6 is going to complicate things. Especially when Facebook blames most things on "user confusion." What's confusing about the fact a program rewrote your entire address book without authorisation?