Your own comment seems to suggest that the cost of the death penalty is excessive: It reduces safety by causing innocent people to die, it reduces safety by making those criminals have nothing left to fear (and probably building a fair bit of resentment), it's expensive due to bureaucratic practices, and it's expensive because you lose all the resources invested in to that individual with no chance of redeeming them in to a productive member of society.

So, I suppose we're in agreement that it's not actually a practical solution for either the goal of safety or finances, even if some people might assume it is? :)