Do I accept as fact that polonium is radioactive? Yes. Do I accept as fact that radioactive elements are poisonous to humans when absorbed? Yes. Do I accept as fact that Polonium from inhaled smoke particles will be absorbed? Yes.
Which part do you see as an unjustified belief?
I understand this thread started with you objecting to the assumption that polonium is harmful to humans. Going so far as to suggest that anything short of an RCT is not enough.
Yet even if I read RCT results concluding polonium to be harmless, I would distrust that conclusion, not my understanding.
Somehow we're doing this epistemology thing differently. It feels to me like you live in a world of impossibly high standards. Or you just like to argue hypotheticals.
The logical positivism part. It brings with it a host of assumptions. Of course, you're free to believe in them, but I don't think logical positivism is justifiable. That's generally why science today is built on falsifiability rather than verifiability.