Scientific (style) inquiry doesn't require that one have no preconceived notions, only that he be willing to be proven wrong about his preconceived notions. It is unfortunately difficult for outsiders to judge whether Snowden cherry-picked or is accurately representing what he found.

But why does this not increase Snowden's credibility? He went undercover to gather evidence of malfeasance. How does that not turn him from a leaker into an investigative journalist getting an inside scoop?