What opinions does Casy espouse about sin and "bad words" in The Grapes of Wrath?

Casy says that profanity is necessary at times as a means
of letting a person vent. Regarding sin, Casy comes to the conclusion that sin is just
"things people do". 

This is a radical opinion for the time
- and it is today too, for that matter - and it marks Casy as a free-thinking, liberal
who is striving to establish his own philosophies on behavior, morality, and religion.
These traits are certainly not negatively presented and seem, in the abstract, to
represent Steinbeck's social values rather precisely as he tended toward a position of
social progressivism. Casy, in this regard, is a champion of Steinbeck's positive
views. 

He is
honest, compassionate, and courageous. Casy’s new “religion” is based on love and a
belief in each person’s soul as well as an all-inclusive soul, the “Holy Spirit” of
humanity.

Casy struggles to
put these things together into a coherent system of thought, but he is always gathering
in new information from his experiences, which makes the process dynamic but also
difficult and troubling for him.