I don't want to derail the thread, but the "no first development" principle I'm suggesting could probably apply to most technologies that are explicitly weapons. It just matters more when it's a giant WMD that is specifically and explicitly designed to exterminate large civilian populations. I'm not going to when someone makes a slightly better gun.

It's true that peaceful and military technologies are interconnected, and that military technologies vary greatly in purpose and effect. There are no clean objective lines. Clearly there are a lot of things that could be individually discussed. But the fact that there's no perfectly rational place to draw the line does not absolve us of responsibility to draw lines (see also: the age of consent). In general, I think humanity should adopt a broad cultural principle of thinking about the long term and aggregate consequences of our actions. This goes deeper than any one issue or technology.

With regards to the nukes in particular, I think it's actually the nuke defenders who are using the meta knowledge that we weren't wiped out. Arms races are a predictable occurrence, WWII featured targeting civilians as a common strategy, and Opp would have known about the development of long range ballistic missiles. So a rational person could definitely have predicted a giant long-range nuclear standoff (with potential for massive destruction) as one major possibility, and a slow trend of many nuclear weapons uses against individual cities as another.