Manning didn't. Drake and the other previous NSA whistleblowers tried the channels and got nowhere. Snowden didn't feel like he had channels to go through.

And when Snowden saw what happened to Manning, what did you think he was going to do? He's not stupid.

If the penalty for disclosing secrets is a year in jail, and it's normal jail, and that jail's run professionally, and not a gladiator school, or an Abu Ghraib, then maybe more people like Snowden would be happy to suck it up and serve a sentence.

But when Manning gets supermaxed, Jose Padilla gets tortured, countless other prisoners are routinely subjected to beatings, rape, random shankings, guards instigating prisoners to assault each other, deprivation of medical care, etc. etc. etc., one concludes that America's prison system has turned into medieval dungeons, and you'd have to be crazy to allow yourself to be subjected to that.

Otherwise...