In case you're not familiar with the term theodicy, it is defined as the vindication of God's goodness and authority in the presence of evil. A common theodicy Christian apologists offer is that God must allow evil to allow good because good cannot exist without evil. I submit that this theodicy is logically flawed. To see what I mean, consider the following argument:
We need good in the world.We can't have good without evil.Therefore, we must endure evil to experience good.
The second premise needs to be shown to be valid. So if we let G represent "good" and ¬G represent "not good" or "evil" and ⊢ be the symbol for "therefore," then the second premise can be formalized:
G ⊢ ¬G.
It's easy to prove that this form is not valid not only for G but for any proposition. Using a truth table, premise G can be true yet the conclusion ¬G can be false! Because an argument is only valid if its conclusion is always true when the premise(s) are true, this argument is not valid.
In other words, if good is the case, then evil need not follow.
Jesus usefully observes that " only God is good". Let's say that only God exists. Therefore evil doesn't exist, but more importantly, evil is a pointless, effectively meaningless term.
We live and think in dualistic terminology. For there to be polarity, there must be TWO poles. You can't have one without the other. If there is no polar opposite to good, then there is no frame of reference to determine what is good.
For example, if we have an infinitely or transcendent good God, by comparison everything else is pure evil. A Gandhi or mother Teresa is just as evil as a Pol Pot or a Stalin in relation to an infinitely good God.
However, from the perspective of someone who is evil, the distance between Gandhi and a mass murderer is significant. The contrast is night and day.
Western philosophy's logic is dualistic. So while good can exist without evil, it cannot meaningfully or logically exist without evil. Do you see the difference? If evil doesn't exist, the concept of evil becomes redundant or pointless right along with the concept of good as well.