This question seemed authentic and caring enough that I wanted to try and answer it from my point of view, as I greatly share your desire to build stronger bridges with people and understand others.
> Do you think unbeing is preferable to a potentially miserable life that would still likely result in them having their own children that didn't experience their own level of suffering?
It would depend on my confidence levels that N recursive generations would have better or worse outcomes. This may sound heartless, but knowing my kid has a better life than me only goes so far in making me feel like suffering is worth that. To me at least, humanity and the world is in a context that I don't see the problems that have caused suffering in my life improving, and while I've never been actively suicidal, the thought that eventually I will un-be again is extremely comforting, to the extent that I don't think I'd regret never-having-been, even outside the tautological that I wouldn't be alive to regret it.
> How many generations of potential suffering is required before having children is off the table? How many n+ future generations of having potentially joyful and regenerating lives would offset the former generations of suffering?
To me at least this question only relevantly includes "those alive while I'm alive." Whether my great great great grandchildren have an amazing time of it has very little bearing on my ability or desire to withstand suffering to achieve it. I realize this is philosophical and subjective.
> What level or type of disaster would trigger it? Would you have had kids if you knew that the Black Death was coming or, being a Roman citizen, that the Roman Empire was going to fall? If you were a European in 1920, fully knowing the outcome of WWII, would you intentionally have kids? What if you only had models that these things were coming in a fuzzy way?
It's less about a specific disaster and more "how much of your life will you get to spend on things that bring you fulfillment and happiness vs. things that cause suffering." If I had reasonably high confidence those specific things you listed were coming I would not have had children, and given my own family's history through those events, I would find myself rather justified in hindsight in doing so. (multiple prisoners of war, multiple international displacements, multiple individuals killed as civilians due to who or what they were.)
In the current context, it has more to do with the holistic "how much of human societal effort do we spend on improving our ability to find joy, actualize ourselves, pursue art, science, and betterment of all human life." And while I recognize that on many absolute measures (e.g. murder) we're better off, it seems to be in the sense of, yes, a society of individuals optimized to serve a relentless machine of efficiency operating a scale far beyond what human group psychology is well-built to interact with, will likely see those same outcomes, but I'm not sure it leads to a net-positive world. A reasonable rebuttal would be if I would ever in history have found life sufficient, given these constraints, and I'm not honestly sure. I can't put myself in a world where I don't have the knowledge and context I do now without feeling I'm lying to myself, but I do think that the presence or absence of the hope that things are going to be "better" vs "more of the same/worse" plays into it heavily (in which sense, innocence may have been bliss), but for better or worse in the current world I do not see the things I value coming any more into the fore.
(I had previously worked jobs that were much more relaxed, to try and leave me more time for the things I value, but finding out I had a chronic condition requiring regular surgery meant that this was effectively not an option, and in the long-term, I would have been in a precarious financial and life position sooner or later had I not anyway.)
> Like, my position is that I'd like to think that I'd undergo torture for my kids, and that my kids would do so likewise for theirs recursively until the number of generations outnumbered the stars.
This gets to the core of the difference between our perspectives, I think. I don't see any inherent good in this outcome. In fact, knowing what I do about human nature/human psychology, that outcome scares the hell out of me. If anything I see "I don't want to have kids" as the one real lever I have to push back against or not be a part of the perpetuation of systems that have gotten us to the point we're at. (While things like climate change are certainly important, to be clear, my lament is largely along things like consolidation of power, the iron law of oligarchy, capture of systems by special interests, and the overarching paperclip-maximizer/"angry tribes of apes" tendencies of humankind)