Father Skywalker said:

Use the death star to rule the galaxy?? What?? I don't get it.... Fear was used to keep the rebels in line, not the people.....No rebels, no death stars, rebels are not good guys, they provoked the war and the destruction of planets.

"No star system will dare oppose the emperor now"

"Fear will keep the local systems in line.... Fear of this battlestation"

It was built to control the people since they had dissolved the senate, NOT built to keep the rebels in line.