I changed my mind
I was initially in the "of course we bloody well should" camp when I first heard about this, but commenters on past articles convinced me otherwise.
I'd like to know if a pardon is legally equal to "you were wrongly convicted" or to "it's okay you broke the law, we'll let you off"?
Neither is appropriate as the first is revisionist - Turing broke the law of the time, and he admitted to being a homosexual. The conviction was therefore entirely legal and correct.
The latter allows someone who is clever / famous / politically of the moment / did some good stuff to get around the law. Turing will not benefit, but it's a cynical ploy and sets a terrible precedent.
it's not the same, I know, but if Jessica Ennis, or a medal winning soldier commit a crime today, should we or a.future government grant them a pardon or immunity?
Instead, I believe strongly that the conviction should stand as a poignant reminder that as a brilliant man was treated horribly and driven to suicide by the nation, and a government just because he was gay... despite working to fight for his country, and against genocide.
That many people, less well known but equally important in their own right, suffered similarly. That there existed such a terrible law in living memory.
Hopefully it won't rise again, and we will fight against similar laws elsewhere.
The best course would surely to be to declare all convictions spent if they aren't already, and to allow survivors to wipe their records of the conviction (if it still shows up), so that it no longer affects them.
Also a cross party / parliamentary commitment to repeal discriminating legislation and prevent any future such laws being passed.
We unfortunately don't have a constitution into which that can be set in stone, but at least they promised...