"Ivan Karamazov said that if God does not exist everything is permitted..."

"... and traditional legal thinkers are likely to say that if legalism (legal formalism, orthodox legal reasoning, a 'government of laws not men,' the 'rule of law' ... and so forth) does not exist everything is permitted to judges — so watch out!"

Richard Posner in "How Judges Think" (quoted by Jac).

TANGENTIALLY RELATED: Christopher Hitchens and Dr. William Lane Craig debate the question “Does God Exist?” and Craig gives 5 arguments for the existence of God, the third one being:

3. The Moral Argument; If God does not exist, then objective moral values do not exist. Rape isn’t just culturally unacceptable, it’s actually wrong.