My impression is that you are attempting to make up a rule about something that is a matter of art and context — situations that are endlessly variable and subtly different. Sometimes the biography of a thinker may be relevant to an introductory discussion, sometimes not.

In an hour and 15 minute introductory lecture, Hubert Dreyfus mentions Heidegger’s Nazism for all of about 2 minutes.

In this lecture, which I think is a public lecture to a general audience, I’m not certain but you can tell from the beginning that its intention is introductory, Mary-Jane Rubenstein mentions very little about Heidegger’s biography at all.