Look at the situation from the perspective of someone who doesn't believe that the US government is tyrannical, and instead, represents the best, most just system in the world.
From that perspective, why wouldn't Snowden stay in the United States, since he's guaranteed the right to a fair trial? Why not face the music at home, instead of fleeing to HK?
Acknowledgement of the leak demonstrates knowledge that the US government is actively violating the constitutional rights of citizens. Assuming it is the most "just system" in the world where one is "guaranteed the right to a fair trial" contradicts that (an assumption that the government will not violate rights).
From that perspective, why wouldn't Snowden stay in the United States, since he's guaranteed the right to a fair trial? Why not face the music at home, instead of fleeing to HK?