Id recommend to see the facts:
--- was it and is it a life threat?
--- was it harmful in any physical way, and what's so emotionally harmful in that took place TECHNICALLY?
Maybe it was abuse of the sort, like threats, I'm going to tell your Mom we're doing nasty things, if you refuse to continue that?
A good psychological councelling must wipe this out.
Your son's state may be due to overinflated feeling of guilt due to widespread social and religious standards, related to this subject, so it's a different thing.