> Resistant to centralized censorship (as you pointed out)
I'd wager that most people don't care about this much, though it is real. Still, this can be achieved with signature-based authentication that doesn't require the tremendous waste of BTC. Just... tell the service your public key and sign a message when you sign up. Your key pair doesn't need to be associated with some distributed system for that to work. This has been around for decades and not exactly caught on.
> It allows you to use the same passphrase for all services without compromising security since your passphrase never needs to leave your own machine; it is never sent over the wire. You just send signatures to different services.
This is true for all signature-based authentication, which does not necessitate a blockchain.
> The cost associated with purchasing tokens needed to initialize an account on the blockchain would serve as a spam prevention mechanism; an alternative to SIM cards which most centralized services rely on today to limit the creation of spam accounts.
This sounds like an anti-feature to me. Especially since it'd be foolish for a service to only support authentication via a blockchain. Imagine telling my grandmother that she needed to buy some btc in order to sign up for the service that hosted my wedding photos.