Some discussion already exists in the Human Rights thread. My thoughts on punishment is that the minimum goal is repair the damage done. So for example, in a simple fender bender car accident, the person at fault pays for the repairs on both cars. Some losses can't be repayed however, like the loss of life. In that case, harsh punishments are justified. The goal in that case is more of deterrent than anything else though.
As for the trolley image, John and Mark did not do the same thing. Assuming both trolleys keep going, John has killed a person. Mark did not. This isn't to say that being drunk while operating machinery is something to be accepted, but harm only occurs when a person causes damage. Compare Mark's trolley trip to one made by a sober driver that doesn't hit anyone and a sober driver that does hit someone.