There's a balance. Complete transparency and access to all information (ie, Julian Assange's stance) is extreme. If we gave away all of our secrets, we wouldn't have an advantage over our country's enemies.
You think Bill Gates should be more transparent with his wealth? Do you think JP Morgan Chase be more transparent about future financial opportunities its pursuing? Do you think China should be more transparent with their economy?
Yeah, it would be great if it would happen, but it won't. Human nature is just too strong for people to willing give up their secrets. Besides, Assange's hate of the US is well documented. For him, it was more of a personal crusade, then trying to create more transparency.
I am not sure that's the case. If we credibly give away all our secrets then we have the advantage that we are viewed as trustworthy - popular support can mean a lot. Sort of like the theory that we developed a moral intuition because being a "good person" is sometimes the most effective way of convincing people you're a "good person".
Whether this advantage could actually be realized, and whether its magnitude is actually greater than that realized by keeping secrets, and whether the difference is important and worth the other costs, are all very much up for debate though.
Particulars don't need to be known (troop locations, battle plans, weapons capabilities/vulnerabilities, list of undercover agents in the field, specific espionage and surveillance techniques, etc), but the fact that it is happening at all should be well known and open for public comment.
Otherwise "consent of the governed" is thrown out the window.