When 'the founders' "sere setting up the criminal justice system long ago", "The Founders believed whipping and other forms of corporal punishment effectively promoted pro-social and discouraged anti-social behavior."
 
" Starting in 1776, Gen. George Washington strongly advocated and utilized JCP in the Continental Army, with due process protection, obtaining in 1776 authority from the Continental Congress to impose 100 lashes, more than the previous limit of 39."
" Thomas Jefferson provided up to 15 lashes for witchcraft, at the jury’s discretion; castration for men guilty of rape, polygamy or sodomy, and a minimum half-inch hole bored in the nose cartilage of women convicted of those sex crimes."

The expensiveness of criminal prosecution was a non-issue.  It cost little to administer the punishments of the time.

You are displaying either your youth, your lack of historical knowledge, or both. 

What you 'believe' about the types of cases being plea-bargained is irrelevant.