It just occurred to me when reading about Sophie Scholl: governments that suppress dissenting speech are making a huge strategic error. I can see why they would have an interest in silencing people who want to publicize shameful things that the government prefers to keep secret, but making an example out of the person who says, "The Supreme Leader sucks! Down with the Supreme Leader!" is counterproductive.
Chilling everyone into silence isn't the same thing as gaining support. It just creates the illusion of a supportive populace, an illusion that fools no one but the leader himself. The people still resent the leader; they just do it silently. The leader doesn't really know who his true supporters are except by their deeds of valor and voluntary sacrifice, because they sound exactly the same as his opponents.
In a society that allows free (or mostly free) speech, the leader knows who his enemies are. The more overt you allow them to be, the easier they are to monitor and, if necessary, to locate. Also, by allowing people to speak their complaints freely (so long as the words don't lead to actions of consequence), you immediately dull the edge of those complaints. "The leader can't be as horrible a tyrant as that, or you wouldn't be allowed to speak those words. REAL tyrants kill people for saying stuff like you just said."
It's for this reason that a tyrant who wishes to be effective must maintain a distinction between the military and the police, unless the populace has long been accustomed to being policed by their army. Concentration camps and other military detention facilities are for enemies of the leader. But civilian prisons and jails are for bad people. Nobody wants to be seen as a bad person. Few are sympathetic to criminals. People will protest for the release of a political prisoner from a place like Guantanamo, but a person convicted in a court of law on charges of attempted murder and conspiring with terrorists will have few friends. In this way, a tyrant can dispose of huge numbers of people. Thousands die in American prisons and jails every year, but we don't call them death camps. Thinking of the American criminal justice system as a form of genocide is considered radical, despite the fact that the poor and minorities--African-American men, especially--are incarcerated at such a higher rate than everyone else. Does anyone doubt that when you're in prison, you're twice as likely to die as when you're free?
We can learn something from Milgram's experiment here. If an armored troop transport rolled down the street with loudspeakers blaring an announcement that all [choose a minority group] are being rounded up and should immediately surrender themselves for a merciful execution, there'd be a battle. Even people who aren't members of the group would be shooting from their windows. The soldiers or police would be regarded as invaders in that instance. But if it's done under the pretense that those people have done something wrong, it suddenly becomes more acceptable. That is, if a few police officers show up at the homes of all the members of a particular religion to arrest them on warrants of violating tax laws or some obscure ordinance about moral turpitude, nobody will interfere.
Likewise, if armed government agents went into a slum and ordered everyone to vacate their homes so the government could bulldoze them and build expensive homes for rich people who would pay more in taxes, there would be resistance. People would fight to keep from being removed. But if the government just raised the taxes on the slum properties enough, a lot of the residents would leave because they couldn't pay. Their homes would fail to sell, and eventually the government would seize the abandoned properties. Those who remained would fall behind in their tax payments. Nobody's going to bat an eye at a bunch of "tax protesters" or "deadbeats" or "slumlords" who were millions of dollars behind on their property taxes having their homes foreclosed on by the county. And then when those people are out on the street, nobody's going to bat an eye at them being arrested for vagrancy.
As such, the successful tyrant is one who can not only convince his people that they are free, but can convince his victims (or at least all witnesses to the victimization) that they got what they deserved. A successful tyrant convinces his people that tyranny is justice.