You guys are seriously jumping straight to torturing ourselves for a niche defense stat? Doesn't make sense to me unless you just want to be edgy.
Paladins.
Also entertainment. Both in the amusing 'What'll she do next?' factor, and the more somber existential character exploration.
I've always embraced character insanity in AN quests because it makes it more enjoyable. To me at least.
It helps that the 'nightmare' cube is likely going to provide the type of madness we missed out on from the early death of Shapers. This won't be the adhd of Harzivan, or the 'get out of my head' deal with Dia's index. This'll be more of a 'why am I doing this, is it all worth it? what's even real?' Type of deal, which hits closest to home and which I suspect AN could write write well.
Edgy is if you're trying to look cool or get attention.
I'm just trying to influence the quest to be entertaining; it's why we're all voting, and why votes often conflict. We all seek out entertainment according to our own values. Sometimes we manage to convince each other.
Alright, I've been arguing primarily from a meta-perspective about madness. If you aren't buying it, I can switch to in-quest reasoning instead.
I think this'll provide the best reward, and, despite appearances to the contrary, the
smallest risk. This is something we can control. Something we can use or discard at will.
This is, effectively, that psyker cube for none psykers. We train with it, we boost skills. We leave it alone, it gathers dust.
Instead of solving it and getting a force-sword, it gives us madness, which is incentive to use it less and avoid the all-too-common power creep of such a choice.
So to summarize:
It gives us power
It avoids power creep
It's entirely within our control
Even the potential negative effects are interesting from a meta-perspective