[ETH_start]

It's easier and more secure than using a password. Public key cryptography in general is a much better way to do authentication than usernames/passwords. This is just leveraging the existing public key infrastructure and wallet software suite of the Ethereum space to create a community with hopefully a critical mass of users able to authenticate themselves with public key cryptography.

Perhaps another minor additional benefit of making it Ethereum-based is that the Ethereum Name Service allows easy use and registration of human-friendly names as proxies for the public keys.

[Animats]

That's not the problem for something in the blog/message board/social network space. The problem is the ability to generate huge numbers of fake identities and spam. You can make all the Etherium wallets you want.

This is the standard spam problem.

[ETH_start]

That's a separate problem, and largely the same whether the sign up method is email or Ethereum account authentication. Spammers can always secure huge numbers of Facebook-accounts/email-addresses/etc.

What this does is make sign in easier and more secure, and obviate the need to keep track of passwords.