"Motivation" means jack-squat in world where powerful entities can buy, steal, or subpoena Google's stash of your personal data. And it's no longer just your data, but involves your entire social-graph. Say, you write to your sister about your father's health in great detail, because you chose to "share" your data with Google, now you're sharing his health information as well, and whoever steals or buys this information (remember, Google is a commercial entity) has it.