Of course God knew what would happen if they used their freedom the wrong way: apparently He thought it worth the risk. Perhaps we feel inclined to disagree with Him. But there is a difficulty about disagreeing with God. He is the source from which all your reasoning power comes: you could not be right and He wrong any more than a stream can rise higher than its own source. When you are arguing against Him you are arguing against the very power that makes you able to argue at all: it is like cutting off the branch you are sitting on. If God thinks this state of war in the universe a price worth paying for free will—that is, for making a live world in which creatures can do real good or harm and something of real importance can happen, instead of a toy world which only moves when He pulls the strings—then we may take it it is worth paying.
Quotes from Mere Christianity, Part 18
C.S. Lewis, Mere Christianity (1952; Harper Collins: 2001) 48.