Full Idea
If one of two contraries be infinite, the other would be altogether destroyed. But the name God means that He is infinite goodness. If therefore God existed there would be no evil discoverable; but there is evil in the world. Therefore God does not exist.
Gist of Idea
God does not exist, because He is infinite and good, and so no evil should be discoverable
Source
Thomas Aquinas (Summa Theologicae [1265], Ia,Q02,Art3,Ob1)
Book Reference
'The Existence of God', ed/tr. Hick,John [Macmillan 1964], p.82
A Reaction
This is not, of course, the opinion of Aquinas. I love the way he states the opposition's arguments so lucidly. The modern problem usually talks of God's omnipotence, rather than infinity. His formulation allows that there might be undiscoverable evil.
Related Idea
Idea 21274 It is part of God's supreme goodness that He brings good even out of evil [Aquinas]