No one who steals your Facebook password can get into anything as serious as your entire medical history. The proposal is dangerous precisely because it's centralized — in the sense of centralizing all different types of data on a particular individual. It also, as a side effect of giving the user more control, would give the user more to lose if their account is compromised. Again, with no clear gain for most people.
I feel we're just going to disagree over this but it's probably because neither of us has clearly stated the threat models we're dealing with. Also, it's somewhat hyperbolic to claim that such proposals are 'dangerous'. I could claim the same about the current situation where more and more personal data is handed over to companies, almost by default.
