The Apple
It seems that within Death Note itself, there are a great deal of allusions to different things. Twice, I’ve noticed that there are what seems like Bible references. The second one is the apples that Ryuk likes, as well as the apples in pictures with Light in them. I may or may not be wrong, but I’m reminded of the story of Adam and Eve. Again, I don’t believe in the religion, I’m simply stating the reference.
The apple had, in the Bible, been a symbol of temptation. In much the same way, so was the Death Note, as Light himself states that the note seemed to have an aura that tempted him to try it at least once. Like there was a whispering in his ear to just try it. All the same in the situation with the apple that tainted humanity. It’s actually stated that from the moment he touched the Death Note on, his life was tainted — ruined by temptation and power.
At first it had started with an innocent teenager thinking he could change the world for the better and make it a less rotten place — and given, he was a little less innocent because he did it due to being bored — by killing criminals. As time went on, he became more warped, and he developed the god complex we all know he has. By the end of the manga/anime, he’s fallen into complete insanity because his temptation had corrupted him beyond repair. Funny, he said that the world was regressing — the world is rotten — when he himself was the one regressing from a state of sanity, to insanity. He ultimately became rotten, like an apple left without being eaten for an incredibly long time.
Also, the highly intelligent are also closer to the brink of insanity than those of lesser intelligence. Too much for the brain to process without falling over a brink where morals become warped and intelligence is used the wrong way.
Crime. It's common to let it be, or leave it to the police, is it not? Has one ever considered that they are... inefficient? The notebook... the Death Note... it came into my possession so I could properly punish evildoers.