To actually answer the question, I think wiping Kurn's memory was a very un-Kahless thing to do. It does not restore his honor, it only placates him in the here and now. When he crosses the river of blood, he would do so as Kurn and will still be dishonored. Worf might as well have let him commit suicide.
Another way to look at it is like this; What would Martok say about it? I bet Worf would never want him to find out what he did to his own brother. From a Klingon standpoint, it was a dishonorable thing to do. From a Starfleet standpoint it was a violation of the person's rights to do that without their permission.
It would do them no good to stain the reputation of their only housebroken Klingon at a time when the role of said Klingon as an on-the-spot mediator was a crucial one.
I literally LOL'ed at that. This is how I'm going to refer to Worf henceforward.