Assange summarised: "the Internet, our greatest tool for emancipation, has been transformed into the most dangerous facilitator of totalitarianism we have ever seen".
Julian is a programmer who runs a server hosting "Wikileaks", which allows uploads of (pertinent/leaked) information Without Moderation - which is easily argued to be "free speech" and whistle blowing (a completely legal activity).
Julian would not have known the significance of a renegade upload until after a complaint was filed unless he read all uploads before posting. Many websites, including Youtube, do not moderate uploads until there is a complaint upon them.
Julian could not have known the clearance and Julian followed industry standard practice (ie, that Google uses).