1. networks where global reach to total strangers is not even possible, or at least is not the default. the vast majority of people only really want to reach their “friends of friends” anyway. this eliminates a lot of would-be hackers from even knowing you exist.
2. accounts that are unhackable because users log in with private keys instead of user/pass that sit on a server. of course losing your private key is a problem, but i would suggest a system of social-account recovery anyway where you can regain access by 3 out of 5 friends approving, for example.