You're comment is absolutely accurate, and why politicians I respect are in short supply.
Success as a politician almost requires you suppress facts that would harm your favored policies, such as "innocents will suffer".
And in fact, as a leader, you could argue that if you are a "good" person (and who among us thinks of ourselves otherwise) and *you* have carefully evaluated both sides and deemed a policy desirable, then aren't you committing evil by spending effort to admit the costs of that policy and thus make it less likely to pass? If you truly think that war is required to reduce suffering in the end, isn't your moral obligation and your duty to suppress (or at the very least, not promulgate) the facts that might diminish support for war?
(And this applies to any policy - healthcare, justice, etc.)
It's a reason that I could never be a politician. I'm selfish enough that I value my morality more than the benefits to the populace that compromising that morality might bring. As a non-entity, my words, harmful though they might be to my own side, are inconsequential.
So, I suppose I came on strong because the disclosure of costs is what I feel morality requires. However, you are quite correct, what we can expect, and what indeed, in some circumstances, may constitute good leadership is quite different. Assumptions of complete rationality are both factually incorrect, and probably make bad policy.