Here's a great post at The Guardian by Ally Fogg on why the pardon is "entirely, profoundly wrong" though it "will be welcomed by many", and is "undoubtedly a gesture of humanity, compassion and progressive values."
In announcing the pardon today, the justice secretary, Chris Grayling, said: "A pardon from the Queen is a fitting tribute to an exceptional man." Turing was certainly an exceptional man but the tribute could not be less fitting. It says that the British state is prepared to forgive historical homosexual acts providing they were performed by a national hero, academic giant or world-changing innovator. This is the polar opposite of the correct message. Turing should be forgiven not because he was a modern legend, but because he did absolutely nothing wrong. The only wrong was the venality of the law. It was wrong when it was used against Oscar Wilde, it was wrong when it was used against Turing and it was wrong when it was used against an estimated 75,000 other men, whether they were famous playwrights and scientists or squaddies, plumbers or office clerks. Each of those men was just as unfairly persecuted, and many suffered similarly awful fates. To single out Turing is to say these men are less deserving of justice because they were somehow less exceptional. That cannot be right. [Bold emphasis added]
[The royal pardon arrived within weeks of the Naz Foundation verdict that it is constitutional (again) to prosecute gays Section 377. See this post by Siddarth Narrain at Kafila unpacking the "unreason" of the Supreme Court judgement. See also the relevant posts (too many to link directly to) at Law and Other Things.]