Oh you silly Americans. The department of homeland security can't do stuff because Assange isn't even an American citizen. The absolute best the government could muster was an attempt to levy rape charges against him. Wikileaks isn't hosted on one server, they're scattered throughout most of Europe and now there are hundreds of volunteers offering to mirror it, so taking it down is virtually impossible.
This information being out in the open is a good thing. The government doesn't keep secrets to keep people safe, it keeps secrets to maintain face. The two are closely related, sure, but it's an important distinction to make. And quite frankly, this glimpse into the world of diplomacy is fascinating.
so Why does this guy do this? is he just trollin?
Fame, probably. Julian Assange is the face of Wikileaks now. I somewhat doubt he's doing it because it's the 'right' thing to do. With an organization like this, though, the motives of the individual are irrelevant. Assange isn't the only one behind Wikileaks, and there are countless people who support the mission. So long as people believe that the governments of the world should be open, I'm sure we'll continue to see leaks.
The release of the cables wasn't a, "Ha ha, let's see how much we can forget up your diplomatic efforts!" but rather a wake-up call. The people should know what their government is up to.