I would believe the "lives in danger" argument, but I can't see any evidence that this is actually the case. Who's life has been put in danger? Has anyone directly been killed or injured by leaks?
The goal is open, honest and accountable government - a worthy cause. Some of the content may look risky, but it is worth the risk for that goal, and without any evidence, "lives in danger" just sounds like the line delivered by the governments who are scared stiff.
As for Assange - is it important if he's a douche? I haven't judged him that way myself, but even if he's trying to do the right thing for the wrong reasons, he's still trying to do the right thing.