I agree with you! There are a lot of things that present non-zero existential risk. I think that my argument is fine as an intellectual exercise, but if you want to use it to advocate for particular policies then you need to make a comparative risk vs. reward assessment just as you say.

Personally, I think the risk is quite large, and enough to justify a significant expenditure of resources. (Although I'm not quite sure how to use those resources to reduce risk...) But this definitely is not implied by the minimal argument.