Lavabit was a service that effectively held keys for its users and was compelled to disclose them. If we were discussing whether a vulnerable service was somehow compelled by the USG, I wouldn't argue. I doubt you'd even need an NSL compromise Lavabit; you might even be able to do it with routine civil litigation. Don't ever use things like Lavabit. That's why we talk about "end to end encryption", as opposed to the bad kind of encryption.