Sorry, I'm not following your first point. The relevant "specific attribute" that sadism and masochism seem to have in this context are that they specifically squick User:gattsuru. If you're trying to claim something else is objectively bad about them, you've not communicated.

I'm not predisposed toward child-raising, but from my understanding the point of "good parent" does not value making someone weak: it values making someone strong.

Yes, and my comparison stands; you specified a person who valued teaching and protecting people, not someone who valued having the experience of teaching and protecting people. Someone with the former desires isn't going to be happy if the people they're teaching don't get stronger. You seem to be envisaging some maximally perverse hybrid of preference-satisfaction and wireheading, where I don't actually value really truly teaching someone, but instead of cheaply feeding me delusions, someone's making actual minds for me to fail to teach!

the vast majority of immortals (artificial or uploaded) stay within a fairly limited set of experiences and values based on their initial valueset.

We are definitely working from very different assumptions here. "stay within a fairly limited set of experiences and values based on their initial valueset" describes, well, anything recognisable as a person. The alternative to that is not a magical being of perfect freedom; it's being the dude from Permutation City randomly preferring to carve table legs for a century.

In that particular case, the equilibrium is less bounded. Butterscotch isn't able to become better than David or even to desire becoming better than David, and a number of pathways for David's desire to learn or teach can collapse such that Butterscotch would not be able to become better or desire becoming better than herself.

I don't think that's what we're given in the story, though. If Butterscotch is made such that she desires self-improvement, then we know that David's desires cannot in fact collapse in such a way, because otherwise she would have been made differently. Agreed that it's a problem if the creator is less omniscient, though.

That's not really the case the other way around. Someone who wants a mentor that knows more than them has to have an unbounded future in the FiOverse, both for themselves and their mentor.

Butterscotch is that person. That is my point about symmetry.

I don't have the right to say that Lars' fate is wrong -- it at least gets close to the catgirl volcano threshold -- but it's shallow enough to be concerning. This sort of thing isn't quite wireheading, but it's close enough to be hard to tell the precise difference.

But then - what do you want to happen? Presumably you think it is possible for a Lars to actually exist. But from elsewhere in your comment, you don't want an outside optimiser to step in and make them less "shallow", and you seem dubious about even the ability to give consent. Would you deem it more authentic to simulate angst und bange unto the end of time?