Also worth seeing that less has to be fundamentally safe at some point, otherwise background radiation would be a threat. If examined on its own without considering the surrounding inert volume, one decaying particle is presumably quite radioactive.

So since less->magically safer is true some point, the argument can't be made fallacious by asserting it is true. The worst the argument can be is unpersuasive (although it is persuasive - from a practical perspective there is a tiny volume of toxic waste, it isn't a reason to block progress).