I think it’s a good thing. It doesn’t accomplish anything tangible, since most of the people are long dead, but symbolic gestures can be important. It’s an acknowledgment that morals have changed and that most of society no longer thinks people should be held criminally liable for some consensual buggery, and additionally that such prosecutions in the past were fundamentally unjust.
It’s true that laws are not the same as morals, but laws change all the time without rendering past criminal convictions null.
The UK repealed its gross indecency statute in 1967; the movement for posthumous pardons for those crimes is much more recent. That indicates to me that the primary motivation for the pardons is the recognition that the law was morally wrong and unjust.
I’ve seen friends hauled off and interrogated, then thrown out of the military for it, and I myself have been interrogated just for knowing them. It’s scary and just fucking ridiculous to be treated like some WWII commie spy over it. And of course the interrogators are just the slimiest scumbags you ever met and they lie their asses off.
It’s basically a legal mechanism by which the executive reverses a conviction. The executive might do so because it’s satisfied that you were wrongly convicted - you never, in fact, committed the acts with which you were charged. Or it might do so because, as an act of mercy or for other policy reasons, it feels you should not be punished (or further punished) for what you did. Or (as in this case) while you did commit the acts and they did constitute a crime at the time, it was unjust that those acts were criminalised and it would be a continuing injustice to label you a convict or to impose any continuing or further punishment on you as a convict.