Alan Turing was judged and convicted by the laws of his time. We can apologise, but not overturn his conviction.

In my lifetime, rather more so than in the earlier decades of the twentieth century before I was born, we have as a nation become more tolerant and more socially liberal. At the same time there has been an increase in regulations and prohibitions. There is a paradox here and there will not be absolute consensus about what has been unbanned nor about what has been banned! But personally I think we've got it about right. Decriminalising homosexuality I support, as I do the prohibition of smoking in public places. Tightening up on drink driving seems to have been right to me, but I also support the reform of the licensing hours for pubs. There's not much, if anything, I'd like to be able to do that is now banned. There's not much I'd like tighter controls over.

So the laws change over time. But at any one time we have to obey those laws - even if we believe they are iniquitous. You can't smoke in a pub, so don't be a dick and try and do so! That's not how it works in a civilised society.

Which brings me to Alan Turing. What he did broke the law and he was convicted and punished. From today's perspective what happened to Turing is shocking - as was the persecution of other homosexuals at that time. But wrong though we now say (rightly in my view) that law was it was then the law and Turing and all the others broke it. If you try and find a way to pardon Turing you have to pardon others as well (Peter Tatchell is currently arguing in favour of this). You cannot discriminate in Turing's favour because he is now famous. Justice is blindly impartial, or should be.

We cannot as a nation get into some huge exercise of retrospectively looking at criminal cases and deciding whether we should overturn convictions. (This is not saying we shouldn't review unsafe convictions - those where it was not the law that was wrong but the conviction against that law). We cannot say that a law that applied in, say, 1950 shouldn't have applied because the law was subsequently repealed. Sadly we can't unhang a murderer who was executed because capital punishment was later abolished. 

I see no problem, in principle, in our generation apologising for the "sins" (as we now see it) of an earlier generation. But we cannot retrospectively change the law and decide that someone duly convicted by due process of law should now be unconvicted.