It seems obvious, to me, but I guess I'll spell it out:
Facebook wants access to your email so badly that they're willing to steal it. This is, in my opinion, among the worst things they've ever done for user privacy (and security, but mostly privacy in this case), in a long list of subtle, and not-so-subtle tactics.
It also has very real security consequences. The automatic contact list updates for potentially millions of users means that sensitive information is likely flowing into facebook servers as we speak, without users knowing it. Passwords, medical information, company secrets, who knows what else? Someone who trusts facebook enough to use it for social interactions might not trust them enough to know about their medical conditions, proprietary company data, passwords for other sites, etc. Facebook took away that privilege for many people with this change.
All that said, here's what's important: This does nothing good for users, and a few bad things. The fact that facebook made this change, knowing that the vast majority of users were not interested in using facebook email thus far, tells us that facebook thinks first of facebook. Even if there were no privacy or security concerns, what the user wants wasn't even in the equation, when facebook did the math on this.