You're right in theory, but in practice, being in favor of retributive "justice" tends to go hand in hand with an acceptance of arbitrary application of said "j

You're right in theory, but in practice, being in favor of retributive "justice" tends to go hand in hand with an acceptance of arbitrary application of said "justice", for reasons typically along the lines of "if you wanted humane treatment then you should've thought about that before being a hard-bitten criminal scumbag" (exaggerating, obviously, but not by much).