I agree that his goal was changing policy. Nevertheless he does not have the power to make policy on his own. The power to change policy rests ultimately in the democratic process. And giving the public the info required to make good policy seems pretty fair to me. The public could have chosen/can choose to ignore his leaks.
Snowden is very explicit that his goal was not to drive policy in any particular direction, only to allow informed, democratic debate about what the NSA is doing. He decided to come forward when he saw that the NSA lies to its congressional oversight committee, which is completely undemocratic.
The NSA is very explicit that their goal is to perform legal surveillance to safeguard the security of the US. Since the truth is secret, to believe either party's goals are as they say is purely a matter of trust.
The NSA has been proven to lie to its overseers repeatedly over the course of decades while Snowden has been proven to lie to the NSA in order to expose its lies. Personally, I regard Snowden's behavior to be more trustworthy in this respect.
He's not making policy. He's informing the public.