According to my dictionary (New Oxford American, 2<sup>e</sup>), the phrase **in itself** means

> viewed in its essential qualities; considered separately from other things

Plug in this meaning into your sentence, and you will see why it makes sense the way it is. You may also come across the hackneyed *in and of itself*, which means the same thing, as in:

> Life, *in and of itself*, is neither good nor evil…

Using only *itself* would also work, but then the emphasis on *life* would not be as strong and it would not have quite the same meaning:

> Life *itself* is neither good nor evil. 

*Itself* merely functions as a pronoun for emphasis. *In itself*, however, adds more depth, as it specifically indicates the subject is being deliberately considered in all its possible ramifications.