What happened to Alan Turing was disgraceful and shameful but I agree with this decision.
We cannot take our contemporary views and laws and impose them on the past. To do so seems almost Orwellian and sinister.
What, if for some reason, the age of consent was raised to 19 in the future. Would people want anyone who had sex with an 18 year old in the past charged with statutory rape? No, of course not. The law as it stands on a particular day should be a matter of fact, not opinion at a later date as to whether it was a 'good' law or not.
It is right that people are aware that the laws as they stand are immutable. Any doubt with regards to that will undermine the rule of law and make people less inclined to obey the law in the hope that any conviction will get overturned at a later date as society comes round to their way of thinking. People must have a strong degree of certainty when it comes to the law of the land.
Lastly, whenever I think of Alan Turing I always feel a little sad. What happened to him was tragic and most certainly to any right thinking person today, anachronistic. It angers me that the law was as it was in the 50's, but it does serve to remind me of how far we have come and how, in so many ways, we are a much better society now. Changing laws retrospectively would allow these injustices to be swept under the carpet.
To my mind Alan Turing was a brilliant man who did as much to win the war as any other individual and the law as it stood then was wrong. Changing the law retrospectively will do nothing to alter those facts in my eyes. I'm afraid to say this wasn't a miscarriage of justice but instead a law that was, by modern standards, wrong. On that basis the verdict should stand and Turing should continue to act as a reminder of how much more tolerant we have become as a society - a fitting legacy and one that I am sure he would be proud of.