If you honestly would personally go to jail rather than comply with a warrant, that speaks pretty highly to your credit, but I don't think most people would find Facebook to be particularly culpable here.
This would be more compelling point if FB were a person capable of going to jail and/or did not have a history of taking the user-hostile side of privacy situations, regardless of whether the law agreed with them.
That isn't the default setting though, and it's unfortunate that the people involved here weren't aware of it.
This right here is why I personally believe FB deserves and flak they get from this situation. They could avoid the whole conversation about whether they should turn over the conversations if they made it so they couldn't. They've chosen their data mine over user privacy, and people are right to judge them accordingly.