On casting blame

There is a story in the New Testament. 

It involves a woman who has committed adultery, about to be stoned to death by a large crowd. She is backed up against the hard, sun-baked wall; the crowd gather around her, loud and swarming. Red dust dances in the air, whipped up by their frenzy. Dusty stones are clutched in hundreds of calloused hands. The crowd asks Jesus what they should do with the woman, for in the Bible it says that a woman who commits adultery should be stoned with death.

We all know of the answer. 

“Let him who is without sin among you be the first to  throw a stone at her.”

Julian Baggini in Should You Judge this Book by its Cover? takes a look at this famous saying and examines its meaning in a modern context.

We usually take this story as a wise fable on the immorality of casting blame on others when we ourselves know what it's like to have been in the wrong. Essentially it says; don't judge others. 
But as Baggini points out, we can't take this saying too literally. Just because none of us are free of 'sin' doesn't mean we should allow people who have commited crimes to go free. There has to be a certain level of judgement. We cannot simply put everyone on the same level, and say that judges shouldn't be allowed to give people sentences because they're not exactly saints themselves. 
If we did follow this story to the latter, we'd be in a society where people are never blamed or judged for the things they do, because everyone's done something.
Perhaps this is one of the reasons we have laws; if noone can be trusted to judge others, if everyone is one and the same because everyone has done something bad at least once, then not a single person can pass judgement on other people. Not a single person can say who should die and who should be imprisoned and who should be pardoned. But the law is blameless, and judges everyone equally. It sets out the lines in the sand. But does this go against the original Bible story? The crowd asks Jesus if the woman should be stoned because in the Old Testament Moses commanded in the law that adulterers should be stoned to death in punishment. 

So how should we reinterpret this famous saying? 
In our current world we do believe that some should have the powers to judge others, to cast blame. Judges, policemen, politicians and law makers. Juries; randomly chosen people who make a decision on whether another person should be blamed for their sin.
What this story teaches us, then, today, is not about punishment but about the wrongness of superfluous blame; the importance of treating others fairly because we all make mistakes and we all do stupid things. 
But then this leads to another question, about what it means to 'treat someone fairly'. What should the definition of fair be? When is enough punishment enough? And should we be considering other methods to rehabilitate those who have done wrong rather than straight-out damning or forgiving them?(Consider the death penalty, China's "reeducation through labour" program, therapy, rehab)
I'll talk about that another day. This Bible story is at least interesting as a concept, and also as a thought experiment on how we interpret different sayings and how these interpretations change(or not.)