And please understand that I'm not arguing who's right, the Soul Hunter or the Minbari. Or whether the soul exists or not, or what it is. I'm just pointing out that there are some built-in contradictions in the Soul Hunters' own claims of what they're doing.
And that makes me think they were sold a bill of goods by whoever put them on the task in the first place.
Whoever said a belief has to be logical and consistent? Soul Hunters are hardly infallible.