Sure you can - I and others just did, in fact, say he was not justified in telling someone.
Further, the actions of others does not necessarily remove their fault from the equation. Even if the military fleet was sent to conquer an entire world in an unprovoked assault of nothing less than pure colonial intent, they did not attack soldiers like the Race did. They did not attack strategically located targets to try to cause the war to end quicker and force the oppositions submission like the Race did. They perpetrated the wholesale slaughter of civilians as they slept.
This is both answering the wrong question again (this is not about Warren) and also wrong on the face of it. The Lizards nuked Berlin and Washington purely as terror tactics to break humanity's will. They unleashed nuclear weapons against the population centers of Australia as a step towards depopulating the continent. The Race perpetrated the wholesale slaughter of civilians as they slept.
Its possible to justify Warren's actions, as I'm sure he did to himself in the fictitious work, but this does not mean that it is righteous by any measurable standard. Yeager's actions are more justifiable than Warren's, but you can still disagree with them because they are, by all accounts, treasonous just as much as you can agree with his objection to obvious genocide and the succeeding coverup.
Warren's actions aren't really justifiable by reasonable standards, either, but that's a whole different thread. Yeager's actions were beyond merely treasonous... one can understand his anger at Warren's actions, but the consequences of revealing it injures far, far more innocent parties than silence.