I honestly can't believe why anyone thought this after he published the first thing that put Wikileaks on the map, the embarrassing Collateral Murder video.
It's funny because before that came out, I considered donating money to Wikileaks because I thought it'd be more like an organization like Wikipedia. I wouldn't be surprised if a lot of people were seduced by the name "Wikileaks" piggybacking off the credibility and mission of Wikipedia.
I guess no one had any critical thinking skills or were prone to conspiracy because everyone from progressives to libertarians started eating everything he did up.
EDIT: Wow just did a search on HN to see what people said back then about it and it seems a few people had the same take I did.