I thought this post was great, in the Slashdot thread about Julian Assange, the (Australian!) man behind Wikileaks:
Secrecy is entrusted to the government on the assumption that it will only be used when truly needed.
However the same power can be and is abused to subvert the freedom of its own people, as misappropriation for personal gain by powerful people and used to cover up ineffective, improper, illegal or immoral activity.
Whistle blowers object to these abuses and fight against it in the only way possible, by removing the shroud of secrecy and revealing these violations of trust to the public.
Mistakes may be made, but revealing the abuse of trust by the government is vital to the continuation of freedom and democracy.
Source – user Nadaka. I Googled the text and it seems to be original, not a quote – I thought it was a good, concise summary about why Wikileaks is handy.