@evildictaitor: It's a interesting idea but it's simply not robust enough. If the two private keys are ever compromised all data that's ever been encrypted using that software is open to all comers. This doesn't just mean my paranoid secrets - this means my social security information some civil servant left on a CD on a train; my bank details that, for reasons known only to my bank, were on an employees laptop that got nicked and so on and so forth. This isn't just about dodgy states, paranoid geeks and the odd paedophile; this about encryption being useless to protect against the very criminal masses everyone accepts we should be protected from. And the very, very real consequences are far worse than a couple of terrorists attacks (in fact easy identify fraud plays directly into terrorists hands).
And is it reasonable to assume that they keys would be compromised? Well industry doesn't have a great record on this. And it turns out the government can't keep secrets either. I am seriously worried that Edward Snowden 2.0 might not be the public spirited whistleblower that Edward Snowden is. The last thing I want is him giving away the key to my data to the Russian, the Chinese or cybercrimeebay.com.
And, finally, you're missing a vital legal point here: the presumption of innocence. I do not, and should not, have to justify my actions without some kind of probable cause. Without evidence to the contrary we must presume that I, you and Joe down the road are not terrorists. And that means, that without evidence, we simply have no right to access, to demand access to or to demand the ability to access their data "just in case". And the result of encryption without an easy back door - that my historic communications are very difficult for the government to access - is not new. In the old days I'd have burnt the private documents or shredded them. The Royal Mail didn't keep routine records of my communications. Now Google do. If I PGP all my messages then I'm simply moving things back to how they were (the authorities are still in a better place because they can get the meta data).