> There is no research I’m aware of on people for whom the prospect of punishment did act as a deterrent (i.e. people who decided not to commit the crime).

Surely this can’t be true - as a trivial example I would be surprised if removing parking fines wouldn’t increase parking violations, or if Singapore stopped punishing littering that it wouldn’t affect the amount of littering etc

Maybe the difference between a 10 year or 20 year sentence for murder doesn’t make much difference, but if murder had no punishment at all I would be very surprised if that wouldn’t raise the murder rate!