Right, well, let's look at it this way -- how much and what kind of harm does the Slayer Oath deal to each King Ironfist?
It's probably a huge shame and stress on them. That probably has social considerations... though given it's been centuries and the deed and circumstances have themselves become mythologized, and also become somewhat accepted, and the Ironfists are treated differently from the way other Slayers are treated... it seems plain to see that an Ironfist Slayer is viewed differently from a normal random Slayer in Dwarf society.
So, how maladaptive an institution is it, actually?
If he can still function as a King -- albeit feeling shitty, and knowing he'd have to leave that shame for his kids, and his kids' kids, and so on -- then... that still functions. You might say that that feeling of shame is counter-productive -- especially because it might result in some people deciding not to have kids and thus potentially there goes the whole thing. Except that goes into the feeling of responsibility that Dwarfs have; they'll have 4 kids as necessary as they feel the responsibility strongly too.
So how do you say that the Slayer Oath as an institution is maladaptive? Or that the Ironfist thing is a maladaptive institution?
Because the Dwarfs as a whole are bothered by Slayers and Slayerdom?
But that's a human perspective. It's an external perspective, too. One held by somebody who does not have the values of the civilization, or race, involved. And also does not hold the psychology of the race and culture to boot too.
Let me ask something else; what if it's not Slayerhood that makes Dwarfs and the Karaz Ankor miserable, what if it's the circumstances and all the troubles and problems of the Warhammer World that make them miserable?
What if the reason they feel miserable is because they took a series of bad blows, which felt like they continued on for millennia?
Maybe the solution to that is to not care about what happened to their civilization, their culture, their heritage, their very lineage, their very religion too. That is easy for us in the real world to say; it's harder for a Dwarf to say or feel, especially if they are a Karaz Ankor dwarf.
Too, as I keep hammering on about this, Dwarf psychology and the requirements of keeping up Divine Great Works/Precursor Tech might require having institutions (and peoples/psychologies) who can keep things going for millennia; which require standards commensurate with that task and challenge. All to live in a difficult and challenging world with magic Chaos daemons and Goblins and other foes.
You cannot just toss away one part of Dwarf society and assume that Dwarf society would be able to improve and get out of its tailspin; and then assume that they can then put that brick back into their society and start being as maximally responsible as before.
And yes, I am thinking that Slayerhood -- or rather, the things that surround Slayerhood and Slayer Oaths and that might lead to Dwarfs taking them, to feeling strongly enough about their failures that they do this -- are all big things that connect to either Dwarf psychology, or to Dwarf culture or to institutions that keep some of their ancient things running.
I'm assuming that while a given Slayer Oath might not be necessary, the fact that Slayerhood exists, or that the Ironfists became Slayer Kings after some great failure, all have reasons. Both reasons in terms of why it happened, and also why and how it connects to Dwarf society/culture/psychology.
But if one doesn't believe in Dwarf social values, or doesn't agree or think Dwarf psychology (and the culture that came from it) necessarily might result in something like that... then one would not find any acceptable reason for things like Slayer Oaths to begin with. And so there would be no way to really explain it, because you'd be working on entirely different foundations or assumptions.
