Assange has no legal duty to cover up US war crimes—and once he possessed the information, he had every ethical obligation to expose those war crimes. In a fair trial, the US would have no right to prosecute Assange or Chelsea Manning for exposing US war crimes. The very suggestion that it was wrong, on any level, for US war crimes to be exposed has to be one of the most perverse corruptions of ethics, morality, and law that you will ever encounter. It boils down to making the obstruction of justice, justice itself.
For more, please read:
https://zeroanthropology.net/2019/04/29/wikileaks-and-julian-assange-the-duty-to-expose-war-crimes/