I would say the use case is to not become a Snowden. "The public" doesn't really mean anything (reference some of Ayn Rand's work) because it abstracts away the individual. Individuals other than Snowden have just as much reason to use Tor as Snowden by virtue of the fact that Snowden has to. That's the whole point. If we had nothing to fear then sure, no one would need to. Snowden proved that everyone has something to fear. Hence Tor.