It's unnecessary. Why would someone email my Facebook instead of emailing me? If they want to send a Facebook message, there's this nifty button called 'Message' for that very purpose. Facebook is Microsoft circa 2003.
Facebook has a billion users, and it's not at all inconceivable that this feature would be useful to a large quantity of them. I suspect that many users, especially younger ones, are more connected and engaged with their Facebook account that with their email. Certainly many Facebook users send far more Facebook messages than emails. Facebook is similar to Microsoft circa 2003 in the sense that a single tech-savvy individual is not their sole concern in product design.
