This is a longstanding and widely accepted ethical and legal principle. However, with the modern emphasis on victims' rights, I suspect many want to abandon this maxim, and to substitute revenge for justice. See this from a classic case of death from delayed brain bleed after a single punch and banging of the head on the ground (Evening Standard Oct 8th p.32): "Judge Anthony Bate told him:"You punched George because he got in your way. The length of the punishment now imposed in no way equates to the enduring and profound loss felt by George's family. You lashed out at him in a moment of hot temper"". So is it fair that someone is punished for the unforeseen (and unforeseeable?) result of a trivial or commonplace act?