The people that run that killing power are also citizens, and they either must be bought at an increasing steep price, or they will go with the bulk of the nation (mostly with their near and distant relatives who are suffering) - network effects are very real here.
Most dictatorships make no less than a half-hearted attempt to convince the population to support them.
And then they make a point out of terrorizing the people who don't support them. Just so the others have no trouble discerning whether believing them is a good idea or not.
It's a very valid concern, but technological advances are also available to the people. Asymmetrics war (terrorism, depending the side you're on) is always a possibility, unless the gap between the possibility of states and those of citizens grows too wide.
