The reverse halo effect you describe is called the horns effect.

Old people, & people immersed in the traditional wisdom of old cultures, believe many things that have playtested as useful beliefs over a very long period. It doesn't follow from this that no dross creeps in.

What I'm puzzled by is the paralell between the violent use of magical cooling against Draco & the preservative use of it on Hermione.

The laws of Wizarding society are, broadly speaking, insane. There is a vast gulf between twisting or breaking a rule that makes no sense and violating the trust of a friend like Hermione.

Circumventing Horcruxes would be one option, certainly. Harry has already thought how blindingly stupid it is that the killing curse must be cast using hate in order to work. If he were going to change anything about it I would imagine that that observation would feature.

There are people in the world who can have their whole day ruined by the mention of rape. It's why we have things like trigger-warnings.

I was only thinking of the trial scene, I'm afraid.

I do wonder whether the Source of Magic, or whatever it is that determines whether a Horcrux can be made, draws a distinction between deaths in combat, deaths accidentally caused and deaths deliberately and avoidably caused.

You're correct, but I was responding to the whole statement:

I wouldn't want to rule out the possibility that Dumbledore deemed himself indispensable >and his soul's contiguousness dispensable to the war effort.

If our dear Headmaster murdered Narcissa because he thought his continued availability to Magical Britain was more important than avoiding that kind of atrocity, or keeping his soul whole then that means that he used the murder to protect himself from death, and in this context that means that he made a Horcrux.

This is, of course, all conjecture. We don't know for certain that Dumbledore himself did the deed, or that it went down the way that the surviving Malfoys believe it did. We do know that Dumbledore finds it useful for them to believe it, and we do know that he has studied how horcruxes are made as part of his Anti-Voldemort campaign, and we can be fairly sure that Madame Bones knows the truth of the matter of Narcissa's death

I hadn't previously seen any clear motive for Dumbledore to kill Narcissa. That he might have done so to help keep himself ready to defend Magical Britain at least provides a possible explanation.

Assuming that he did, in fact, do broadly what Draco said, anyhow.

Pedanterrific, I'm not conflating the two acts, merely observing that one may illuminate the other.