You have grossly underestimated the number of people that luke killed. Even with a population of 32 billion the station would be mostly void of life, making it very vunerable to sabatage. For more check out http://www.theforce.net/swtc "The duration of the superlaser strike on Alderaan was about 0.21s (although it took slightly more than a second for the weapon to build up energy before the beam was released). Therefore the power of this beam, which needs to exceed the power dissipation rate of any deflector shields of the target, is at least of the order of 1032 W. In A New Hope the original Death Star was able to generate at least this amount of energy and to replenish it within the few days which transpired between the destruction of Alderaan and the Battle of Yavin. According to The Death Star Technical Companion, the Death Star was capable of generating sufficient energy for a full planetary disruption in a single day. Thus the main reactor was capable of generating energy beyond the station's continual running needs at a base rate of at least 2x1027 Watts. This power is approximately five times the continuous output of the Sun. It is vastly in excess of any artificial power source known to any other major fictional universe."