Peck Knew More Than Kathy About God: On What Basis?

In my latest reading of The Road Less Traveled: A New Psychology of Love, Traditional Values and Spiritual Growth, M. Scott Peck talks about religion and spirituality.  He discusses three case studies: a woman named Kathy who was weighed down by her Catholic views on sin and guilt, a woman named Marcia who had anti-religious parents and did not enjoy life, and a man named Theodore who was skeptical about religion but became more religious after he had addressed issues from his past, namely, being bullied by his siblings and his parents' tendency to take away things that he valued when they punished him.  While Peck acknowledges that religion can have negative psychological effects, as it did in the case of Kathy, he criticizes psychotherapy's overall antagonism towards religion.  He says that science itself has become open to paradox, and that he feels that God has assisted him in his efforts to help people.

There was one time in my latest reading when Peck appeared to be rather arrogant.  Kathy felt that she had to chant continually to appease God, for she was having sexual thoughts about other men and believed that God was displeased with her.  (Peck learned eventually that this was because Kathy's husband was homosexual and thus failed to satisfy his wife's sexual needs.)  But, when Kathy said that she feared that God would kill her for wanting to see an ex-boyfriend, Peck replies that he knows more about God than she does, and he notes that there are plenty of people who cheat on their spouses who are not punished by God.  I thought that Peck's overall argument was effective----although I will say that infidelity can bring its own negative consequences, whether God directly punishes or not----but I considered him to be rather arrogant for claiming that he knew more about God.  On what basis can Peck claim that he knows more about someone who is unseen, one we don't even know for a fact exists?  And how can we even know this being in the first place?  The Bible?  But the Bible contains the theme that God punishes sinners.  Catholics would then say that the church has the authority to interpret the Bible.  But Peck essentially encourages Kathy to question Catholic doctrine about sin and guilt and to start thinking for herself.  Experience?  That may be the basis for Peck's theology, but cannot experience be limited, even subjective at times?

I myself wouldn't jettison the notions of sin and guilt, for I believe that there is right and wrong.  At the same time, I sympathize with a psychotherapy that doesn't condemn but rather tries to find causes for people being unfaithful, while pursuing the patient's healing and reconciliation with his or her spouse.