But then, by your examples one can argue that democracies tend to correct themselves when they go too far.
Democracies correct themselves when the people will it to happen. It is always in the government's/ruling class's interest to try to use their position to keep the power to themselves. If that means throwing people who disagreed with them in jail on trumped up charges, as happened in the McCarthy era, then that's what happens. It is the people in the democracy who must stand up and defend their rights. What brought an end to McCarthyism was not the FBI saying "oh, whoops we went to far". It was Americans, and specifically prominent radio hosts and Hollywood personalities, speaking out against the practice. Which is why what Snowden did is important. Americans can only protest things if they know it exists.
But the government has nothing to worry about. We are living in an age where people care more about who got kicked off American Idol, then the systematic destruction of democracy as we know it. Which is very sad.