That's because your formulation of the principle is too general. If everyone acts on their own subjective law then collective law would break down. But no one is arguing for that.
Wikileak's defenders would do better to point to the particular conditions that have led to mass whistle blowing: permanent wars in the Middle East and North Africa (the US is in seven wars right now); the creation of a massively powerful surveillance state; and the lack of legitimate channels for political and military transparency and accountability.
The case for whistleblowing hinges on that reality.
It's not about whistleblowing it's about hacking a DoD account to access classified military intelligence.
Given Gitmo and the practices disclosed from there the US government seems to follow that rationale