I'm not sure I made myself clear: my position is that the encryption needs to be done on each end-user's PC, not on some centralised service such as Lavabit.
While the USA could extract the secrets from one person, if that person is living in the USA, it is harder fro them to do so to people outside the USA. Although they could burgle people's houses and extract information that way, it doesn't scale and they certainly couldn't do it to all the people in a country.
How would facebook (or the non US equivalent) work if data was encrypted on everyone's PC. There is no PKI that would support that at the moment (Although a social network that also acts as a PKI is an interesting idea.)
Lavabit was the middleman in the communication, not the end; or was it?