Full Idea
Perhaps evil is an illusion, or it is necessary for good to exist, or in humans it is required because we have free will, or God lacks the full power to control it, but none of these looks convincing.
Gist of Idea
Is evil an illusion, or a necessary contrast, or uncontrollable, or necessary for human free will?
Source
report of J.L. Mackie (Evil and Omnipotence [1955], §B) by PG - Db (ideas)
Book Reference
'The Philosophy of Religion', ed/tr. Mitchell,Basil [OUP 1971], p.95