You know, a good analogy here I think is the printing press. One could certainly have made the argument at the time that the printing press, and the ability of people to interpret the bible for themselves, would have disastrous consequences. It could have been argued that such would lead to wide scale social destabilization, religious conflict, and the undermining of traditional structures of power, economy, and social order.
And such criticisms would have been spot on. However, from our modern viewpoint, the revolutionary spread of information was a net beneficial thing. One could argue that it lead to the decline of authoritarian religious power and the enlightenment.
I personally have always been an anti-pragmatist when it comes to evaluating the morality of a situation. That is because the long term consequences of actions can never be accurately predicted, and hardly any positive action can avoid having negative consequences for some. I think it's better to evaluate the morality of an individual action based on a priori principles, i.e, murder is wrong, truth is desirable, etc. There are of course, always shades of grey, and I am not going to go so far as saying things like troop movements or weapons schematics shouldn't be kept secret.
I hear from a lot of people that the transparency will make it harder for international systems to functions. To me, if things like bribes, torture, and realpolitik support for shady characters is necessary, perhaps the international system as it exists deserves to die. It is a very dark view of humanity that all these things are necessary, and furthermore that the public is better off not knowing. In a democracy (or republic), theoretically, choices are made based on accurate information. A lot of the information that came out highlights the real costs of our foreign policy; literally, in terms of money, ethically, in terms of what is being done in the name of the US, and perception wise, as far as how our actions are perceived by other countries. How can people make informed choices if they don't have a clear picture of what is occurring?
Increasingly, we deal with a government that claims individual citizens have little right to privacy. From monitoring conversations and financial transcations, to profiling "domestic extremists" for their political views, even to having images of our body available, the notion of personal privacy has changed. Many see it as hypocritical that those in highest office, acting theoretically as servants of the people and funded by our labor, have a double standard for themselves and the "common man."
History has shown that access to information can revolutionize society, and attempts to censor or stifle it fail in the long run. Perhaps the negative reaction is partially a fear of a world that is potentially on the brink of change.
On a final note, many have made ad hominem criticisms of the central character here, Julian Assange. It is often useful to turn a larger political debate into a discussion of one man. I do not believe that even if this man is killed or wikileaks is shut down, the issue of the internet changing what information is kept secret is going away. However, i have think many criticisms of the man are off base. I would like to submit this link to an interview, in which I believe he comes off as very thoughtful.
http://blogs.forbes.com/andygreenberg/2010/11/29/an-interview-with-wikileaks-julian-assange/