> I keep coming back to this to reply but I cant really figure out how to tackle it. Theres so much of a particular view of the world in each statement.

The problem you're running in to is most likely that you asked someone to define a subjective measure. What you then bump into with the anti-nuclear crowd is safety has one standard for most things and then a different, inconsistent standard when "nuclear" gets mentioned. So a level of harm (or cost/benefit to be more precise) that would be fine for say, lead poisoning or car safety would be a shut-down-the-industry event if it involved nuclear material.

And there isn't really a follow up at that point because there is a definitional tautology where, because it involves nuclear material, nuclear material can't be safe. The problem with that is obvious if you want people to have access to clean-cheap-safe power, but it is logically valid and there isn't really a socially acceptably way to have a go at someone for having inconsistent standards if they are happy to own it. And the argument just got derailed away from the actual issues.

The more argumentatively correct line is to ask what level of harm is acceptable for nuclear, get told "zero", then point out that this is a standard that isn't applied to anything else in power generation and that our standards of harm from nuclear power should be consistent with everything else. The argument then isn't over a definition but why they think it is acceptable to have an unreasonable and inconsistent standard (which is the real issue).