It was within the capabilities of 1940s state actors. Even if it still takes a state actor level of resources now, that probably won't remain true all that long

It was within the capabilities of 1940s state actors. Even if it still takes a state actor level of resources now, that probably won't remain true all that long (considering that it's within the capabilities of North Korea, it can't be that far from "large corporation" levels of difficulty even now). I can't think of any obvious examples of other materials that would be reasonable to restrict in the same way as fissile materials though. Those are kind of a special case where there aren't many uses for the material (power and bombs are basically the only uses I'm aware of for enriched uranium), and it's hard enough to obtain that trying to restrict it isn't entirely useless (unlike phosphorous, which you can buy in the grocery store in any box of matches). Chemical weapons I suppose. Since it's an important example, I don't think it's a bad faith argument, but also note that an argument that restrictions on simple possession of one material without any proof of intent to use it for harm are justified doesn't mean that all such restrictions are justified. I think gp was arguing the "sometimes justified" case, not the "always justified" one.