I see. So they can sometimes be accidentally correct in expecting that they are not vulnerable, as in fact they will not be vulnerable, but their level of certainty in that fact will almost certainly ("of course") be off in a systematic predictable way. This interpretation works.

I wasn't making an argument (a series of propositions intended to support a conclusion), I was talking about the subject in passing. These are different modes of communication, and I would have thought it reasonably clear which one was being used.

I think of the "talking about the subject in passing" mode as "making errors, because it's easier that way", which looks to me as a good argument for making errors, but they are still errors.