Was Mark speaking to the early church in terms that they would recognize from their own lives; i.e., were mutilation and drowning punishments used by Romans? Was he warning them that disobedience to Christ would have an even more severe punishment? (I've been reading Morna Hooker).
The punishments listed are dire. Consider the crime--impeding someone's progress. And let us remember verses 38-40--Jesus has a pretty loose definition of following.