What's worse is that the Dimonds forbid that anyone pray for a person who dies and is, in their eyes, guaranteed to be in hell. Unless the Dimonds are blessed with omniscience, they should refrain from their ex cathedra-level declarations on who is in hell.
Well, the truth is in between. Indeed one should not pray publicly for a departed heretic, and the presumption is in fact that they are lost. Dimonds take the presumption a bit too far in one direction, while others minimize the presumption into a mere possibility ... with each side overreacting to the other. When people pray for public heretics or public sinners, there's the danger of minimizing the gravity of heresy, but at the same time the Dimonds tend to carry on as if there's no such thing a purely material heresy. There's a balance there that is not always easy to find.
Let's take the case of a different sin. Let's say that Mel Gibon died suddely tomorrow without having first expressed any sign of repentance for the public state of sin he's in. Church would traditionally have refused Christian burial with the presumption that he died in his sin. If people offered prayers for him pubicly, it should be with the stipulation that they hoped that he would have repented of his sin before death, but would not offer them with the same attitude as if the person had died to all appearances as a practicing Catholic, a faithfuld departed.
I mean, for crying out loud, there were Trad Catholics who were offering prayers when Rush Limbaugh died, and one Motarian group was praying publicly for the departed heretic "Queen" Elizabeth.
At the same time, Joseph Ratzinger was validly baptized a Catholic, and so God have easily provide him the necessary lights and graces to save his soul even in his final moment of life.