One thing is for sure. The CIA could have killed him, could kill him now, if he truly posed a threat to national security. The fact that they don't indicates they don't feel he is a threat. I'm confident that whatever goal posts you claim Snowden set back, I can explain as ultimatley serving US interests. That's the barometer. Has he hurt US Interests? Seems US interests are doing fine to me. Would things be better if he has revealed nothing? Probably not. His revelations are great distractions.

No, they can't kill him now. They're not allowed to by one of only players on Earth they try not to push too hard: Putin, head of Superpower No 2. They weigh the risk against the fact that damage is already done and all they'd protect is further image problems. They're countering that seperately.

Re damage. Tens of billions to economy that military-industrial complex worked hard to get. Push-back against police state legislation. NSA ops and methods blown. Large uptake in products that reduce SIGINT. Businesses moving overseas. All with no benefits on the table for intelligence agencies.

Far as distractions, that's the media's job focing on mass shooters, North Korea, ISIS, etc instead of pending legislation and schemes by government.

They can't kill him now. Assassination would risk public backlash way beyond anything he could say.