It's funny, I've come to think of the HN community as being the most skeptical and contrarian of all internet forums. (Jokingly, to the point that if someone posted a blog about how Hitler was evil, there would be an a reliable proportion of posters here pointing out how the citation free post was rhetorically weak and that there were some little understood benefits to the Nazi regime).
Now, this short excerpt of Assange's argument strikes me as outlandish, and there's only a couple of skeptical posts to be found!
There are a bunch of problems that I can see with it, I'll just list a few off the top of my head.
1) It's a predictive argument, which is hard (prediction). The prediction is that society will become worse because of the internet.
2) Glorification of the past: a casual consideration of societies and governments of the past highlights that they are, all of them, horrible. You don't have to go back far in US history to get to an amazingly evil government (1970s CIA activities for example)
3) The increased transparency brought on by the internet is a good thing. ,I'm glad Petraeus got his ass busted, as the phony hero creation meme has been weakened that provides cover for US misdeeds in the war theaters. Governments have been literally getting away with murder since time immemorial. There is a better chance of stopping them if there is, in general, more public, unencrypted communication (this is precisely what brought Petraeus down)
4) There is no way the public at large is going to start encrypting their communication. That kind of secrecy is just not that useful to the average citizen. It is also too complicated to understand for busy non-hackers.
5) The benefits created by network effects will be significantly diminished by introducing private encryption. One of the main uses of the internet is the creation of large scale markets. Markets are by definition public, or at least open to a group. To get efficient markets you need a sizable group. To keep access to a market private gets harder the more participants it has. Fairly determined efforts to conduct secret, anonymous actions by hacker groups like Anonymous have proved to be easily broken by law enforcement. And these are hackers!
6) Efforts at resisting tyranny can be demonized, and crushed, more readily if conducted in secret. The fact that Wikileaks acted somewhat non-anonymously to release supposedly secret data to public is what made it effective. If Assange had tried to undermine the secret making apparatus of the power structure in secret, he would have been just another terrorist (and maybe dead)
I could go on, but my point is that I think what Assange is promoting here is pointless. I can't even conceive of how private keys could be distributed to a large network without being easily compromised. I would love to hear some of you smarter folk comment on this.