Because with browserID your email acts like a public key, and presumably the third party does a better job at securing your private key (with 2 factor auth, bio

Because with browserID your email acts like a public key, and presumably the third party does a better job at securing your private key (with 2 factor auth, biometrics etc) than most people do on their own (the current password theft onslaught proves that). If this gets traction i m sure many hacker groups will come up with independent, noncommercial and nongovernmental authenticators.