As a blogger, I maintain multiple email accounts. Some accounts I allow to "know" each other, and other accounts I like to keep separate. As a bit of a computer geek, this is just something I do automatically, so that if an account gets hijacked, the damage is limited to only those accounts in the circle of knowledge. Most software subscriptions allow you to confirm that you are the actual email owner upon initial contact. If you do not confirm, then your email account is left alone. Not so Facebook. It seems to be irrelevant to Facebook whether or not the email given really belongs to the person trying to use it. No, their "solution" to people accidentally or on purpose using other email accounts is to force their users to register all their email accounts to their Facebook account. From a data gathering point of view it certainly makes sense, except of course, if an email account is linked by someone who doesn't have access to it, then not so much.