After his confession, Near grins, and everyone else is shocked.
Light asks them if they're going to kill them right here—if they're going to kill the god of the New World. He tells them that the world has changed, and Kira is not considered a mass murderer anymore. In fact, they will be the ones to suffer if they kill him.
He points out that thanks to him the crime rate has dropped 70% worldwide. However, the world is still filled with rotten people who stand in his way of creating a peaceful utopia. Those people who have strayed away from the path of righteousness do not deserve to live. Evil begets more evil and spreads around until it influences the weak of will. If evil is stopped, then the people of the world will begin to change and live in the peace and kindness that they deserve.
When Light first came to possession of the notebook, he knew that he was the only one that can stop the evil in the world. Of course, he knew that killing people is a crime in itself, but it was the only way to do it. If he killed all the rotten, despicable people in the world, the good people of the world would see that punishment that came to those who did evil. Then, the good people would never be come corrupt, thus he would establish a utopia without crime and without evil. So what is wrong with killing harmful people?
His intentions were unselfish! Not once did he think about his own personal gain! He asks everyone if they want to go back to a world where evil can run rampant. Would arresting Kira really be in the best interest of the world? Is it really all just for the sake of Near's ego?
Near continues by saying that he has no right to judge what is right and what is wrong, who is good and who is evil... because in the end, he is not truly a god. He is a human, just like Near.
Realising that his speech had no effect on the others, Light remembers the piece of Death Note that he always has hidden in his watch.
Ohba said that the chapter title "Impossible" was given because of the fact that it is impossible for Light to change the attitudes and feelings of Near and the other people with the speech he made defending himself trying to justify his actions. Ohba added that Light is trying to buy time with a plan that he knows will not work.