The Chronicle of Higher Education has an article
on the Black Notebooks.
Was an apolitical Black Forest professor simply led astray by Hitler for a few years? Or are racist categories at the core of his philosophical convictions? Why didn’t Heidegger in the postwar decades ever once express shock, sadness, or remorse about the murder of Europe’s Jewry?
No, Heidegger led himself astray. Heidegger's anti-cosmopolitanism is rooted in his own circumstances. Had he been born in New York, he would have had a different set of prejudices.
The core of his philosophical thinking (convictions?) is Aristotle. One only has to read Heidegger to know this. For an example of racist categories in philosophy see Kant.
Almost no one in Germany expressed remorse for what happened. See Fassbinder's films about the period. My understanding from reading what's available is that Heidegger had to promote his philosophical insights, to keep them from being misrepresented (e.g., by Sartre). For him to discuss anything else, especially his own biography, would have been a distraction, he thought.
Many of America's philosophy departments were gutted in the McCarthy era, and simply didn't have anyone competent to interpret Heidegger ("What? Learn German and Greek? When I can simply do logic, and still get tenure? Fergeddaboutit!"). Consequently, today, philosophy professor that don't know Aristotle, must continue to justify why one shouldn't read Heidegger, being unable to understand him themselves.