A couple thoughts, somewhat from what I've heard preached before...
This could be asking God not to punish those people in this life for that sin.
This could be asking God to grant forgiveness of this particular sin, and thus they would not receive temporal or eternal punishment for that particular sin.
Of course any of these who died without being born again would still be condemned to hell but perhaps these specific sins would not be a factor in their degree of punishment.
Each or all make logical sense I think