Mens rea is a state of intent, not knowledge.
Suppose, for example, that you discovered a locked storage box with 'property of Big Bank' on the outside. You're supposed to report found items to the police; instead you take it home. Someone sees you and the police turn up; it emerges the box contains a lot of money, and you are charged with theft. You argue at trial that no mens rea existed because you didn't know about the money; true, but the possibility that a locked box belonging to Big Bank would be full of cash was what motivated you to take it home. If, on the other hand, the both contained a brick, you could still be charged with attempt because your intent in picking up the box was impure, even if the contents were valueless.
In this case, Wikileaks 'insurance' documents have in the past contained classified information; they are meant to function as insurance because the contents would embarrass or injure someone if revealed; revelation would be contingent on Wikileaks' dissolution or disablement; and it's reasonable to suppose that only a government could bring that about. Thus, your decision to host the files, even without knowledge of their content, involves an awareness of the strong possibility that they do contain classified information. So whatever the contents actually turn out to be, you would be judged on your intent given the information available at the time.
Now you might also argue that there was some higher interest motivating your actions, eg the belief that all secrecy is evil and that nothing should be classified, ever. But such moral beliefs are normative, ie expressions of what you think the law should be; they have no bearing on what the law actually is, and it is the latter which is supposed to govern your actions. For comparison, I might hold a sincere belief that any insult to a person's honor justifies violent retaliation; but if I kill someone in defense of my honor, that won't spare my from charges of murder, because my private belief is not the law of the land, no matter how sincerely it is held.
In short, don't take deliberately engineered ignorance as equivalent to innocence.
You may find this law review article of interest: http://www.columbialawreview.org/wp-content/uploads/2012/07/... This discusses a narrower reading of mens rea than I have outlined above, but bear in mind the elevated likelihood of a public welfare argument in a case where national security turns out to be at stake. So I would be reluctant to rely on Flores-Figueroa as an escape hatch because that was a case in which the harm largely befell a single individual (the lawful possessor of the identifying information that F-F appropriated), as opposed to the general public whose collective security could be compromised by the release of classified information, personified in the form of the Untied States.