When you do something whose main purpose seems to be to embarrass the U.S. rather than actually expose corruption, what happens? The U.S. loses influence in the world. But who do you think gains influence? Sure some of the less-corrupt democracies do, except their openness means they're vulnerable to the same blind-eye type releases of secrets Wikileaks is conducting. No, the real winners here are totalitarian states which keep a tight lid on their secrets. They gain the most from a system which predominantly exposes the secrets of open societies.
It is my pleasure to point out the vast majority of the above to be false on many levels. Most of the claims has been debunked in so many Slashdot comments today, yesterday and before that you better go and read up. If I repeat it here, it doesn't serve anyone as you could instead just scroll a few posts in any direction and get the same answers there. Instead, I'll comment only a few more unique ways how the above quoted text is misinformend.
When U.S. corruption is exposed, other corrupted governments see that it can happen to them too. Either they clean up their act, or they hurt themselves by adding numerous procedures to avoid leaking that make their own life hard. I quote Assange:
in a world where leaking is easy, secretive or unjust systems are nonlinearly hit relative to open, just systems. Since unjust systems, by their nature induce opponents, and in many places barely have the upper hand, mass leaking leaves them exquisitely vulnerable to those who seek to replace them with more open forms of governance.
Open and just systems have a lot less need for ineffective secretive procedures, and thus for example doubling the security has a very small net effect. Unjust, corrupt systems rely heavily on secrecy, so to increase secrecy, a huge amount of extra expenses and ineffeciency need to be introduced. In short: Not only is it wrong to claim "their openness means they're vulnerable", it is completely the opposite of truth by Assange's logic, which has a lot of merit to it.
US has unsuccesfully tried to keep a tight lid about many of its secrets. Even before the recent lax policy, their secrets have been leaked often and intensively. Check out the cases of Robert Hanssen and Aldrich Ames for two examples and the "see also" sections for more. Any regime more totalitarian than the US has a similar risk running at all times of its operation.
The following could be applied for Russia or any other state you may want to imagine: If some piece of information or volumes of it gets everyone in the country enraged at their government, the government has a lot less means of staying in power than prior to that information leaking. You are correct for claiming that when governments, like China, suppress the information so that their citizens don't know what's going on don't suffer the same effect - but that is only until someone finds a way to leak information through the oppressive Great Firewall or other means employed.
This is more likely happen if any local activists in those countries receive support in form of information, training, resources, connections and any other form from outside. The less our government keeps us in the dark, the more we an concentrate on issues that exist without our government creating them first. Like issues with totalitarian regimes that we wish to do something about.
Prior to Wikileaks the US government had much success in fooling their citizens to think "Do we, the righteous US of A, have power abroad where someone is threatening us? No! Let's attack before they get us!" Now that it's harder for the government to spend more than 1 000 000 000 000 dollars on an unjust war by lying about the reasons for it, people are free to think about something else than what the corrupted government wants them to think.
In fact, Wikileaks paves way for uncorrupt congressmen by removing the secretive advantages that corrupt ones once held. Ladies and gentlemen, I give you Ron Paul:
"Lying is not patriotic" -- "In a free society, we are supposed to know the truth. In a society where truth becomes treason, we are in big trouble" -- "Could it be that the real reason for the near-universal attacks on WikiLeaks is more about secretly maintaining a seriously flawed foreign policy of empire than it is about national security?"