Heidegger's response looks rather weak to me, but note that Marcuse also didn't get his point about the treatment of East Germans by 'one of the Allies':

Not too long ago, I saw an exhibition on the 'Wolfskinder'[1], and what happened there looked pretty genocidal to me (though of course it wasn't the same as the meticulously planned 'Endlösung').

[1] https://en.wikipedia.org/wiki/Wolf_children