[O]n the view that there is no generally privileged position from which to judge whether someone’s beliefs are true, there is no clear general distinction between beliefs and knowledge.
-- Russell Hardin, How Do You Know?: The Economics of Ordinary Knowledge
I'll have to remember this fallacy for the next time I'm teaching intro philosophy students the Metaphysics-Epistemology distinction.
But what do you think is the best way to explain and clear up this misunderstanding? (I might say: "All that follows from our fallibility in judging whether someone's beliefs are true, is that we may be similarly fallible in judging whether their beliefs constitute knowledge. But that's entirely compatible with there being a clear general distinction here, as revealed by the fact that we can perfectly well understand what the underlying difference between the two possibilities would be. It's just to say that we may not be in a position to uncontroversially recognize which of the two we're actually dealing with in any given case." Does that seem clear enough?)