He didn't release it to the public, he chose journalists specifically who had a lot of integrity and would go through the data with lawyers and release only what pertained to the public interest, with the rest being destroyed or kept encrypted. It was also recorded and those recordings are the basis for the "citizenfour" documentary, so you can see for yourself.
You can contrast this cleanly with Wikileaks which usually dumped only barely redacted information - this was a deliberate systemic filtering conducted by neutral journalists; Snowden published literally nothing himself and the vast majority of documents never made it to the public. In fact when he travelled out of Hong Kong he had literally no documents anymore.
I'm not sure what you'd expect him to do honestly.
The abuse of these systems was so systemic and widespread that the nature of them needed to be understood so that the scale of abuse could be comprehended.
If you didn't know what xkeyscore was, then "civil servants spy on people they find attractive, routinely" doesn't have the same sting..
.... if Google engineers didn't know that there was an internal wiretap on the unencrypted part of there network ("data unencrypted and renecrypted here, LOL!" - actual quoted slide) then the push from big tech companies to encrypt internal traffic never happens, then mass surveillance of literally everyones email continues... heck, it probably still did... I'd bet money that they've planted staff who planted backdoors...
So, what didn't he need to leak, point me to.. say, two things.
NSA spying in China? Maybe, but USA spying on Angela Merkel was necessary, because spying on allied politicians is against several agreements. GCHQ leaks were important because it detailed the mechanism in which Five Eyes governments were circumventing their own laws that protect civilian rights to privacy. In fact, it was seeing James Clapper, then Director of National Intelligence, lie in front of the Senate that triggered Snowden to leak things, because it was clear that the laws were not being applied- and everything released reinforces that point.
I hate to be so cynical, but among people who are concerned about privacy and american influence, these findings are sort of like "no surpise the military surveillance state that built the internet for military and surveillance purposes would continue using it for military and surveillance purposes." I mean after all, many of us grew up getting threatening letters from the powers that be saying "hey, we surveilled your network traffic on behalf of the private moneyed interests who own all the IP in this country and found illegal activity." Witch hunts like McCarthy going after communists are public record and known parts of our history. MKultra. COINTELPRO. FBI writing a letter to MLK asking him to kill himself. CIA selling crack. Lying about Vietnam. Lying about Iraq WMDs. This has always been a bit of a banana republic.
The reason practically all sites are HTTPS now can be traced to this. Many, if not most, sites in 2012 were plain http. Which is actually difficult for me to remember despite working on sites as a sysadmin back then.
I don’t think anyone was convicted, maybe some resignations and a lot of very uncomfortable questions from the senate- and likely some policy changes, though I can’t point to them.
As for Snowden? I dunno. The NSA was pretty much breaking the law and everybody knew it. I really want to like and believe in the romantic notion of his actions. But something just doesn't add up with him...