Well, "denying" is used in a more broad sense here, rather than literally claiming it never happened. If he's claiming that less than six million people died, then he *is* denying the events of the Holocaust.And yes, as a historian it is his responsibility to investigate but imagine if, for example, a historian came out with a book that claimed black people didn't get the vote because they were all lazy and never bothered to try to get it... you'd imagine he might be met with some justified criticism, no? You can't hide behind a banner of academic objectivity when you're making claims with no evidence.