Facebook doesn't have to determine whether Bob and Alice are okay sharing an account because doing so is already expressly prohibited by their terms of service[

Facebook doesn't have to determine whether Bob and Alice are okay sharing an account because doing so is already expressly prohibited by their terms of service[0]: > "You will not share your password (or in the case of developers, your secret key), let anyone else access your account, or do anything else that might jeopardize the security of your account." [0]: https://www.facebook.com/terms.php https://www.facebook.com/terms.php